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All rights reserved. .\" Copyright (c) 2011, Pawel Jakub Dawidek .\" Copyright (c) 2012, Glen Barber .\" Copyright (c) 2012, Bryan Drewery .\" Copyright (c) 2013, Steven Hartland .\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved. .\" Copyright (c) 2014, Joyent, Inc. All rights reserved. .\" Copyright (c) 2014 by Adam Stevko. All rights reserved. .\" Copyright (c) 2014 Integros [integros.com] .\" Copyright (c) 2016 Nexenta Systems, Inc. All Rights Reserved. .\" Copyright (c) 2014, Xin LI .\" Copyright (c) 2014-2015, The FreeBSD Foundation, All Rights Reserved. .\" Copyright 2019 Richard Laager. All rights reserved. .\" Copyright 2018 Nexenta Systems, Inc. .\" Copyright 2019 Joyent, Inc. .\" Copyright (c) 2019, Kjeld Schouten-Lebbing .\" .Dd September 1, 2020 .Dt ZFSPROPS 8 .Os Linux .Sh NAME .Nm zfsprops .Nd Native properties and user-defined of ZFS datasets. .Sh DESCRIPTION Properties are divided into two types, native properties and user-defined .Po or .Qq user .Pc properties. Native properties either export internal statistics or control ZFS behavior. In addition, native properties are either editable or read-only. User properties have no effect on ZFS behavior, but you can use them to annotate datasets in a way that is meaningful in your environment. For more information about user properties, see the .Sx User Properties section, below. .Ss Native Properties Every dataset has a set of properties that export statistics about the dataset as well as control various behaviors. Properties are inherited from the parent unless overridden by the child. Some properties apply only to certain types of datasets .Pq file systems, volumes, or snapshots . .Pp The values of numeric properties can be specified using human-readable suffixes .Po for example, .Sy k , .Sy KB , .Sy M , .Sy Gb , and so forth, up to .Sy Z for zettabyte .Pc . The following are all valid .Pq and equal specifications: .Li 1536M, 1.5g, 1.50GB . .Pp The values of non-numeric properties are case sensitive and must be lowercase, except for .Sy mountpoint , .Sy sharenfs , and .Sy sharesmb . .Pp The following native properties consist of read-only statistics about the dataset. These properties can be neither set, nor inherited. Native properties apply to all dataset types unless otherwise noted. .Bl -tag -width "usedbyrefreservation" .It Sy available The amount of space available to the dataset and all its children, assuming that there is no other activity in the pool. Because space is shared within a pool, availability can be limited by any number of factors, including physical pool size, quotas, reservations, or other datasets within the pool. .Pp This property can also be referred to by its shortened column name, .Sy avail . .It Sy compressratio For non-snapshots, the compression ratio achieved for the .Sy used space of this dataset, expressed as a multiplier. The .Sy used property includes descendant datasets, and, for clones, does not include the space shared with the origin snapshot. For snapshots, the .Sy compressratio is the same as the .Sy refcompressratio property. Compression can be turned on by running: .Nm zfs Cm set Sy compression Ns = Ns Sy on Ar dataset . The default value is .Sy off . .It Sy createtxg The transaction group (txg) in which the dataset was created. Bookmarks have the same .Sy createtxg as the snapshot they are initially tied to. This property is suitable for ordering a list of snapshots, e.g. for incremental send and receive. .It Sy creation The time this dataset was created. .It Sy clones For snapshots, this property is a comma-separated list of filesystems or volumes which are clones of this snapshot. The clones' .Sy origin property is this snapshot. If the .Sy clones property is not empty, then this snapshot can not be destroyed .Po even with the .Fl r or .Fl f options .Pc . The roles of origin and clone can be swapped by promoting the clone with the .Nm zfs Cm promote command. .It Sy defer_destroy This property is .Sy on if the snapshot has been marked for deferred destroy by using the .Nm zfs Cm destroy Fl d command. Otherwise, the property is .Sy off . .It Sy encryptionroot For encrypted datasets, indicates where the dataset is currently inheriting its encryption key from. Loading or unloading a key for the .Sy encryptionroot will implicitly load / unload the key for any inheriting datasets (see .Nm zfs Cm load-key and .Nm zfs Cm unload-key for details). Clones will always share an encryption key with their origin. See the .Em Encryption section of .Xr zfs-load-key 8 for details. .It Sy filesystem_count The total number of filesystems and volumes that exist under this location in the dataset tree. This value is only available when a .Sy filesystem_limit has been set somewhere in the tree under which the dataset resides. .It Sy keystatus Indicates if an encryption key is currently loaded into ZFS. The possible values are .Sy none , .Sy available , and .Sy unavailable . See .Nm zfs Cm load-key and .Nm zfs Cm unload-key . .It Sy guid The 64 bit GUID of this dataset or bookmark which does not change over its entire lifetime. When a snapshot is sent to another pool, the received snapshot has the same GUID. Thus, the .Sy guid is suitable to identify a snapshot across pools. .It Sy logicalreferenced The amount of space that is .Qq logically accessible by this dataset. See the .Sy referenced property. The logical space ignores the effect of the .Sy compression and .Sy copies properties, giving a quantity closer to the amount of data that applications see. However, it does include space consumed by metadata. .Pp This property can also be referred to by its shortened column name, .Sy lrefer . .It Sy logicalused The amount of space that is .Qq logically consumed by this dataset and all its descendents. See the .Sy used property. The logical space ignores the effect of the .Sy compression and .Sy copies properties, giving a quantity closer to the amount of data that applications see. However, it does include space consumed by metadata. .Pp This property can also be referred to by its shortened column name, .Sy lused . .It Sy mounted For file systems, indicates whether the file system is currently mounted. This property can be either .Sy yes or .Sy no . .It Sy objsetid A unique identifier for this dataset within the pool. Unlike the dataset's .Sy guid , the .Sy objsetid of a dataset is not transferred to other pools when the snapshot is copied with a send/receive operation. The .Sy objsetid can be reused (for a new dataset) after the dataset is deleted. .It Sy origin For cloned file systems or volumes, the snapshot from which the clone was created. See also the .Sy clones property. .It Sy receive_resume_token For filesystems or volumes which have saved partially-completed state from .Sy zfs receive -s , this opaque token can be provided to .Sy zfs send -t to resume and complete the .Sy zfs receive . .It Sy redact_snaps For bookmarks, this is the list of snapshot guids the bookmark contains a redaction list for. For snapshots, this is the list of snapshot guids the snapshot is redacted with respect to. .It Sy referenced The amount of data that is accessible by this dataset, which may or may not be shared with other datasets in the pool. When a snapshot or clone is created, it initially references the same amount of space as the file system or snapshot it was created from, since its contents are identical. .Pp This property can also be referred to by its shortened column name, .Sy refer . .It Sy refcompressratio The compression ratio achieved for the .Sy referenced space of this dataset, expressed as a multiplier. See also the .Sy compressratio property. .It Sy snapshot_count The total number of snapshots that exist under this location in the dataset tree. This value is only available when a .Sy snapshot_limit has been set somewhere in the tree under which the dataset resides. .It Sy type The type of dataset: .Sy filesystem , .Sy volume , .Sy snapshot , or .Sy bookmark . .It Sy used The amount of space consumed by this dataset and all its descendents. This is the value that is checked against this dataset's quota and reservation. The space used does not include this dataset's reservation, but does take into account the reservations of any descendent datasets. The amount of space that a dataset consumes from its parent, as well as the amount of space that is freed if this dataset is recursively destroyed, is the greater of its space used and its reservation. .Pp The used space of a snapshot .Po see the .Em Snapshots section of .Xr zfsconcepts 8 .Pc is space that is referenced exclusively by this snapshot. If this snapshot is destroyed, the amount of .Sy used space will be freed. Space that is shared by multiple snapshots isn't accounted for in this metric. When a snapshot is destroyed, space that was previously shared with this snapshot can become unique to snapshots adjacent to it, thus changing the used space of those snapshots. The used space of the latest snapshot can also be affected by changes in the file system. Note that the .Sy used space of a snapshot is a subset of the .Sy written space of the snapshot. .Pp The amount of space used, available, or referenced does not take into account pending changes. Pending changes are generally accounted for within a few seconds. Committing a change to a disk using .Xr fsync 2 or .Dv O_SYNC does not necessarily guarantee that the space usage information is updated immediately. .It Sy usedby* The .Sy usedby* properties decompose the .Sy used properties into the various reasons that space is used. Specifically, .Sy used No = .Sy usedbychildren No + .Sy usedbydataset No + .Sy usedbyrefreservation No + .Sy usedbysnapshots . These properties are only available for datasets created on .Nm zpool .Qo version 13 Qc pools. .It Sy usedbychildren The amount of space used by children of this dataset, which would be freed if all the dataset's children were destroyed. .It Sy usedbydataset The amount of space used by this dataset itself, which would be freed if the dataset were destroyed .Po after first removing any .Sy refreservation and destroying any necessary snapshots or descendents .Pc . .It Sy usedbyrefreservation The amount of space used by a .Sy refreservation set on this dataset, which would be freed if the .Sy refreservation was removed. .It Sy usedbysnapshots The amount of space consumed by snapshots of this dataset. In particular, it is the amount of space that would be freed if all of this dataset's snapshots were destroyed. Note that this is not simply the sum of the snapshots' .Sy used properties because space can be shared by multiple snapshots. .It Sy userused Ns @ Ns Em user The amount of space consumed by the specified user in this dataset. Space is charged to the owner of each file, as displayed by .Nm ls Fl l . The amount of space charged is displayed by .Nm du and .Nm ls Fl s . See the .Nm zfs Cm userspace subcommand for more information. .Pp Unprivileged users can access only their own space usage. The root user, or a user who has been granted the .Sy userused privilege with .Nm zfs Cm allow , can access everyone's usage. .Pp The .Sy userused Ns @ Ns Em ... properties are not displayed by .Nm zfs Cm get Sy all . The user's name must be appended after the @ symbol, using one of the following forms: .Bl -bullet -width "" .It .Em POSIX name .Po for example, .Sy joe .Pc .It .Em POSIX numeric ID .Po for example, .Sy 789 .Pc .It .Em SID name .Po for example, .Sy joe.smith@mydomain .Pc .It .Em SID numeric ID .Po for example, .Sy S-1-123-456-789 .Pc .El .Pp Files created on Linux always have POSIX owners. .It Sy userobjused Ns @ Ns Em user The .Sy userobjused property is similar to .Sy userused but instead it counts the number of objects consumed by a user. This property counts all objects allocated on behalf of the user, it may differ from the results of system tools such as .Nm df Fl i . .Pp When the property .Sy xattr=on is set on a file system additional objects will be created per-file to store extended attributes. These additional objects are reflected in the .Sy userobjused value and are counted against the user's .Sy userobjquota . When a file system is configured to use .Sy xattr=sa no additional internal objects are normally required. .It Sy userrefs This property is set to the number of user holds on this snapshot. User holds are set by using the .Nm zfs Cm hold command. .It Sy groupused Ns @ Ns Em group The amount of space consumed by the specified group in this dataset. Space is charged to the group of each file, as displayed by .Nm ls Fl l . See the .Sy userused Ns @ Ns Em user property for more information. .Pp Unprivileged users can only access their own groups' space usage. The root user, or a user who has been granted the .Sy groupused privilege with .Nm zfs Cm allow , can access all groups' usage. .It Sy groupobjused Ns @ Ns Em group The number of objects consumed by the specified group in this dataset. Multiple objects may be charged to the group for each file when extended attributes are in use. See the .Sy userobjused Ns @ Ns Em user property for more information. .Pp Unprivileged users can only access their own groups' space usage. The root user, or a user who has been granted the .Sy groupobjused privilege with .Nm zfs Cm allow , can access all groups' usage. .It Sy projectused Ns @ Ns Em project The amount of space consumed by the specified project in this dataset. Project is identified via the project identifier (ID) that is object-based numeral attribute. An object can inherit the project ID from its parent object (if the parent has the flag of inherit project ID that can be set and changed via .Nm chattr Fl /+P or .Nm zfs project Fl s ) when being created. The privileged user can set and change object's project ID via .Nm chattr Fl p or .Nm zfs project Fl s anytime. Space is charged to the project of each file, as displayed by .Nm lsattr Fl p or .Nm zfs project . See the .Sy userused Ns @ Ns Em user property for more information. .Pp The root user, or a user who has been granted the .Sy projectused privilege with .Nm zfs allow , can access all projects' usage. .It Sy projectobjused Ns @ Ns Em project The .Sy projectobjused is similar to .Sy projectused but instead it counts the number of objects consumed by project. When the property .Sy xattr=on is set on a fileset, ZFS will create additional objects per-file to store extended attributes. These additional objects are reflected in the .Sy projectobjused value and are counted against the project's .Sy projectobjquota . When a filesystem is configured to use .Sy xattr=sa no additional internal objects are required. See the .Sy userobjused Ns @ Ns Em user property for more information. .Pp The root user, or a user who has been granted the .Sy projectobjused privilege with .Nm zfs allow , can access all projects' objects usage. .It Sy volblocksize For volumes, specifies the block size of the volume. The .Sy blocksize cannot be changed once the volume has been written, so it should be set at volume creation time. The default .Sy blocksize for volumes is 8 Kbytes. Any power of 2 from 512 bytes to 128 Kbytes is valid. .Pp This property can also be referred to by its shortened column name, .Sy volblock . .It Sy written The amount of space .Sy referenced by this dataset, that was written since the previous snapshot .Pq i.e. that is not referenced by the previous snapshot . .It Sy written Ns @ Ns Em snapshot The amount of .Sy referenced space written to this dataset since the specified snapshot. This is the space that is referenced by this dataset but was not referenced by the specified snapshot. .Pp The .Em snapshot may be specified as a short snapshot name .Po just the part after the .Sy @ .Pc , in which case it will be interpreted as a snapshot in the same filesystem as this dataset. The .Em snapshot may be a full snapshot name .Po Em filesystem Ns @ Ns Em snapshot Pc , which for clones may be a snapshot in the origin's filesystem .Pq or the origin of the origin's filesystem, etc. .El .Pp The following native properties can be used to change the behavior of a ZFS dataset. .Bl -tag -width "" .It Xo .Sy aclinherit Ns = Ns Sy discard Ns | Ns Sy noallow Ns | Ns .Sy restricted Ns | Ns Sy passthrough Ns | Ns Sy passthrough-x .Xc Controls how ACEs are inherited when files and directories are created. .Bl -tag -width "passthrough-x" .It Sy discard does not inherit any ACEs. .It Sy noallow only inherits inheritable ACEs that specify .Qq deny permissions. .It Sy restricted default, removes the .Sy write_acl and .Sy write_owner permissions when the ACE is inherited. .It Sy passthrough inherits all inheritable ACEs without any modifications. .It Sy passthrough-x same meaning as .Sy passthrough , except that the .Sy owner@ , .Sy group@ , and .Sy everyone@ ACEs inherit the execute permission only if the file creation mode also requests the execute bit. .El .Pp When the property value is set to .Sy passthrough , files are created with a mode determined by the inheritable ACEs. If no inheritable ACEs exist that affect the mode, then the mode is set in accordance to the requested mode from the application. .Pp The .Sy aclinherit property does not apply to POSIX ACLs. .It Xo .Sy aclmode Ns = Ns Sy discard Ns | Ns Sy groupmask Ns | Ns .Sy passthrough Ns | Ns Sy restricted Ns .Xc Controls how an ACL is modified during chmod(2) and how inherited ACEs are modified by the file creation mode. .Bl -tag -width "passthrough" .It Sy discard default, deletes all .Sy ACEs except for those representing the mode of the file or directory requested by .Xr chmod 2 . .It Sy groupmask reduces permissions granted in all .Sy ALLOW entries found in the .Sy ACL such that they are no greater than the group permissions specified by .Xr chmod 2 . .It Sy passthrough indicates that no changes are made to the .Tn ACL other than creating or updating the necessary .Tn ACL entries to represent the new mode of the file or directory. .It Sy restricted will cause the .Xr chmod 2 operation to return an error when used on any file or directory which has a non-trivial .Tn ACL whose entries can not be represented by a mode. .Xr chmod 2 is required to change the set user ID, set group ID, or sticky bits on a file or directory, as they do not have equivalent .Tn ACL entries. In order to use .Xr chmod 2 on a file or directory with a non-trivial .Tn ACL when .Sy aclmode is set to .Sy restricted , you must first remove all .Tn ACL entries which do not represent the current mode. .El .It Sy acltype Ns = Ns Sy off Ns | Ns Sy nfsv4 Ns | Ns Sy posix Controls whether ACLs are enabled and if so what type of ACL to use. When this property is set to a type of ACL not supported by the current platform, the behavior is the same as if it were set to .Sy off . .Bl -tag -width "posixacl" .It Sy off default on Linux, when a file system has the .Sy acltype property set to off then ACLs are disabled. .It Sy noacl an alias for .Sy off .It Sy nfsv4 default on FreeBSD, indicates that NFSv4-style ZFS ACLs should be used. These ACLs can be managed with the .Xr getfacl 1 and .Xr setfacl 1 commands on FreeBSD. The .Sy nfsv4 ZFS ACL type is not yet supported on Linux. .It Sy posix indicates POSIX ACLs should be used. POSIX ACLs are specific to Linux and are not functional on other platforms. POSIX ACLs are stored as an extended attribute and therefore will not overwrite any existing NFSv4 ACLs which may be set. .It Sy posixacl an alias for .Sy posix .El .Pp To obtain the best performance when setting .Sy posix users are strongly encouraged to set the .Sy xattr=sa property. This will result in the POSIX ACL being stored more efficiently on disk. But as a consequence, all new extended attributes will only be accessible from OpenZFS implementations which support the .Sy xattr=sa property. See the .Sy xattr property for more details. .It Sy atime Ns = Ns Sy on Ns | Ns Sy off Controls whether the access time for files is updated when they are read. Turning this property off avoids producing write traffic when reading files and can result in significant performance gains, though it might confuse mailers and other similar utilities. The values .Sy on and .Sy off are equivalent to the .Sy atime and .Sy noatime mount options. The default value is .Sy on . See also .Sy relatime below. .It Sy canmount Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Sy noauto If this property is set to .Sy off , the file system cannot be mounted, and is ignored by .Nm zfs Cm mount Fl a . Setting this property to .Sy off is similar to setting the .Sy mountpoint property to .Sy none , except that the dataset still has a normal .Sy mountpoint property, which can be inherited. Setting this property to .Sy off allows datasets to be used solely as a mechanism to inherit properties. One example of setting .Sy canmount Ns = Ns Sy off is to have two datasets with the same .Sy mountpoint , so that the children of both datasets appear in the same directory, but might have different inherited characteristics. .Pp When set to .Sy noauto , a dataset can only be mounted and unmounted explicitly. The dataset is not mounted automatically when the dataset is created or imported, nor is it mounted by the .Nm zfs Cm mount Fl a command or unmounted by the .Nm zfs Cm unmount Fl a command. .Pp This property is not inherited. .It Xo .Sy checksum Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Sy fletcher2 Ns | Ns .Sy fletcher4 Ns | Ns Sy sha256 Ns | Ns Sy noparity Ns | Ns .Sy sha512 Ns | Ns Sy skein Ns | Ns Sy edonr .Xc Controls the checksum used to verify data integrity. The default value is .Sy on , which automatically selects an appropriate algorithm .Po currently, .Sy fletcher4 , but this may change in future releases .Pc . The value .Sy off disables integrity checking on user data. The value .Sy noparity not only disables integrity but also disables maintaining parity for user data. This setting is used internally by a dump device residing on a RAID-Z pool and should not be used by any other dataset. Disabling checksums is .Sy NOT a recommended practice. .Pp The .Sy sha512 , .Sy skein , and .Sy edonr checksum algorithms require enabling the appropriate features on the pool. FreeBSD does not support the .Sy edonr algorithm. .Pp Please see .Xr zpool-features 5 for more information on these algorithms. .Pp Changing this property affects only newly-written data. .It Xo .Sy compression Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Sy gzip Ns | Ns .Sy gzip- Ns Em N Ns | Ns Sy lz4 Ns | Ns Sy lzjb Ns | Ns Sy zle Ns | Ns Sy zstd Ns | Ns .Sy zstd- Ns Em N Ns | Ns Sy zstd-fast Ns | Ns Sy zstd-fast- Ns Em N .Xc Controls the compression algorithm used for this dataset. .Pp Setting compression to .Sy on indicates that the current default compression algorithm should be used. The default balances compression and decompression speed, with compression ratio and is expected to work well on a wide variety of workloads. Unlike all other settings for this property, .Sy on does not select a fixed compression type. As new compression algorithms are added to ZFS and enabled on a pool, the default compression algorithm may change. The current default compression algorithm is either .Sy lzjb or, if the .Sy lz4_compress feature is enabled, .Sy lz4 . .Pp The .Sy lz4 compression algorithm is a high-performance replacement for the .Sy lzjb algorithm. It features significantly faster compression and decompression, as well as a moderately higher compression ratio than .Sy lzjb , but can only be used on pools with the .Sy lz4_compress feature set to .Sy enabled . See .Xr zpool-features 5 for details on ZFS feature flags and the .Sy lz4_compress feature. .Pp The .Sy lzjb compression algorithm is optimized for performance while providing decent data compression. .Pp The .Sy gzip compression algorithm uses the same compression as the .Xr gzip 1 command. You can specify the .Sy gzip level by using the value .Sy gzip- Ns Em N , where .Em N is an integer from 1 .Pq fastest to 9 .Pq best compression ratio . Currently, .Sy gzip is equivalent to .Sy gzip-6 .Po which is also the default for .Xr gzip 1 .Pc . .Pp The .Sy zstd compression algorithm provides both high compression ratios and good performance. You can specify the .Sy zstd level by using the value .Sy zstd- Ns Em N , where .Em N is an integer from 1 .Pq fastest to 19 .Pq best compression ratio . .Sy zstd is equivalent to .Sy zstd-3 . .Pp Faster speeds at the cost of the compression ratio can be requested by setting a negative .Sy zstd level. This is done using .Sy zstd-fast- Ns Em N , where .Em N is an integer in [1-9,10,20,30,...,100,500,1000] which maps to a negative .Sy zstd level. The lower the level the faster the compression - 1000 provides the fastest compression and lowest compression ratio. .Sy zstd-fast is equivalent to .Sy zstd-fast-1 . .Pp The .Sy zle compression algorithm compresses runs of zeros. .Pp This property can also be referred to by its shortened column name .Sy compress . Changing this property affects only newly-written data. .Pp When any setting except .Sy off is selected, compression will explicitly check for blocks consisting of only zeroes (the NUL byte). When a zero-filled block is detected, it is stored as a hole and not compressed using the indicated compression algorithm. .Pp Any block being compressed must be no larger than 7/8 of its original size after compression, otherwise the compression will not be considered worthwhile and the block saved uncompressed. Note that when the logical block is less than 8 times the disk sector size this effectively reduces the necessary compression ratio; for example 8k blocks on disks with 4k disk sectors must compress to 1/2 or less of their original size. .It Xo .Sy context Ns = Ns Sy none Ns | Ns .Em SELinux_User:SElinux_Role:Selinux_Type:Sensitivity_Level .Xc This flag sets the SELinux context for all files in the file system under a mount point for that file system. See .Xr selinux 8 for more information. .It Xo .Sy fscontext Ns = Ns Sy none Ns | Ns .Em SELinux_User:SElinux_Role:Selinux_Type:Sensitivity_Level .Xc This flag sets the SELinux context for the file system file system being mounted. See .Xr selinux 8 for more information. .It Xo .Sy defcontext Ns = Ns Sy none Ns | Ns .Em SELinux_User:SElinux_Role:Selinux_Type:Sensitivity_Level .Xc This flag sets the SELinux default context for unlabeled files. See .Xr selinux 8 for more information. .It Xo .Sy rootcontext Ns = Ns Sy none Ns | Ns .Em SELinux_User:SElinux_Role:Selinux_Type:Sensitivity_Level .Xc This flag sets the SELinux context for the root inode of the file system. See .Xr selinux 8 for more information. .It Sy copies Ns = Ns Sy 1 Ns | Ns Sy 2 Ns | Ns Sy 3 Controls the number of copies of data stored for this dataset. These copies are in addition to any redundancy provided by the pool, for example, mirroring or RAID-Z. The copies are stored on different disks, if possible. The space used by multiple copies is charged to the associated file and dataset, changing the .Sy used property and counting against quotas and reservations. .Pp Changing this property only affects newly-written data. Therefore, set this property at file system creation time by using the .Fl o Sy copies Ns = Ns Ar N option. .Pp Remember that ZFS will not import a pool with a missing top-level vdev. Do .Sy NOT create, for example a two-disk striped pool and set .Sy copies=2 on some datasets thinking you have setup redundancy for them. When a disk fails you will not be able to import the pool and will have lost all of your data. .Pp Encrypted datasets may not have .Sy copies Ns = Ns Em 3 since the implementation stores some encryption metadata where the third copy would normally be. .It Sy devices Ns = Ns Sy on Ns | Ns Sy off Controls whether device nodes can be opened on this file system. The default value is .Sy on . The values .Sy on and .Sy off are equivalent to the .Sy dev and .Sy nodev mount options. .It Xo .Sy dedup Ns = Ns Sy off Ns | Ns Sy on Ns | Ns Sy verify Ns | Ns .Sy sha256[,verify] Ns | Ns Sy sha512[,verify] Ns | Ns Sy skein[,verify] Ns | Ns .Sy edonr,verify .Xc Configures deduplication for a dataset. The default value is .Sy off . The default deduplication checksum is .Sy sha256 (this may change in the future). When .Sy dedup is enabled, the checksum defined here overrides the .Sy checksum property. Setting the value to .Sy verify has the same effect as the setting .Sy sha256,verify. .Pp If set to .Sy verify , ZFS will do a byte-to-byte comparison in case of two blocks having the same signature to make sure the block contents are identical. Specifying .Sy verify is mandatory for the .Sy edonr algorithm. .Pp Unless necessary, deduplication should NOT be enabled on a system. See the .Em Deduplication section of .Xr zfsconcepts 8 . .It Xo .Sy dnodesize Ns = Ns Sy legacy Ns | Ns Sy auto Ns | Ns Sy 1k Ns | Ns .Sy 2k Ns | Ns Sy 4k Ns | Ns Sy 8k Ns | Ns Sy 16k .Xc Specifies a compatibility mode or literal value for the size of dnodes in the file system. The default value is .Sy legacy . Setting this property to a value other than .Sy legacy requires the large_dnode pool feature to be enabled. .Pp Consider setting .Sy dnodesize to .Sy auto if the dataset uses the .Sy xattr=sa property setting and the workload makes heavy use of extended attributes. This may be applicable to SELinux-enabled systems, Lustre servers, and Samba servers, for example. Literal values are supported for cases where the optimal size is known in advance and for performance testing. .Pp Leave .Sy dnodesize set to .Sy legacy if you need to receive a send stream of this dataset on a pool that doesn't enable the large_dnode feature, or if you need to import this pool on a system that doesn't support the large_dnode feature. .Pp This property can also be referred to by its shortened column name, .Sy dnsize . .It Xo .Sy encryption Ns = Ns Sy off Ns | Ns Sy on Ns | Ns Sy aes-128-ccm Ns | Ns .Sy aes-192-ccm Ns | Ns Sy aes-256-ccm Ns | Ns Sy aes-128-gcm Ns | Ns .Sy aes-192-gcm Ns | Ns Sy aes-256-gcm .Xc Controls the encryption cipher suite (block cipher, key length, and mode) used for this dataset. Requires the .Sy encryption feature to be enabled on the pool. Requires a .Sy keyformat to be set at dataset creation time. .Pp Selecting .Sy encryption Ns = Ns Sy on when creating a dataset indicates that the default encryption suite will be selected, which is currently .Sy aes-256-gcm . In order to provide consistent data protection, encryption must be specified at dataset creation time and it cannot be changed afterwards. .Pp For more details and caveats about encryption see the .Em Encryption section of .Xr zfs-load-key 8 . .It Sy keyformat Ns = Ns Sy raw Ns | Ns Sy hex Ns | Ns Sy passphrase Controls what format the user's encryption key will be provided as. This property is only set when the dataset is encrypted. .Pp Raw keys and hex keys must be 32 bytes long (regardless of the chosen encryption suite) and must be randomly generated. A raw key can be generated with the following command: .Bd -literal # dd if=/dev/urandom of=/path/to/output/key bs=32 count=1 .Ed .Pp Passphrases must be between 8 and 512 bytes long and will be processed through PBKDF2 before being used (see the .Sy pbkdf2iters property). Even though the encryption suite cannot be changed after dataset creation, the keyformat can be with .Nm zfs Cm change-key . .It Xo .Sy keylocation Ns = Ns Sy prompt Ns | Ns Sy file:// Ns Em .Xc Controls where the user's encryption key will be loaded from by default for commands such as .Nm zfs Cm load-key and .Nm zfs Cm mount Cm -l . This property is only set for encrypted datasets which are encryption roots. If unspecified, the default is .Sy prompt. .Pp Even though the encryption suite cannot be changed after dataset creation, the keylocation can be with either .Nm zfs Cm set or .Nm zfs Cm change-key . If .Sy prompt is selected ZFS will ask for the key at the command prompt when it is required to access the encrypted data (see .Nm zfs Cm load-key for details). This setting will also allow the key to be passed in via STDIN, but users should be careful not to place keys which should be kept secret on the command line. If a file URI is selected, the key will be loaded from the specified absolute file path. .It Sy pbkdf2iters Ns = Ns Ar iterations Controls the number of PBKDF2 iterations that a .Sy passphrase encryption key should be run through when processing it into an encryption key. This property is only defined when encryption is enabled and a keyformat of .Sy passphrase is selected. The goal of PBKDF2 is to significantly increase the computational difficulty needed to brute force a user's passphrase. This is accomplished by forcing the attacker to run each passphrase through a computationally expensive hashing function many times before they arrive at the resulting key. A user who actually knows the passphrase will only have to pay this cost once. As CPUs become better at processing, this number should be raised to ensure that a brute force attack is still not possible. The current default is .Sy 350000 and the minimum is .Sy 100000 . This property may be changed with .Nm zfs Cm change-key . .It Sy exec Ns = Ns Sy on Ns | Ns Sy off Controls whether processes can be executed from within this file system. The default value is .Sy on . The values .Sy on and .Sy off are equivalent to the .Sy exec and .Sy noexec mount options. .It Sy filesystem_limit Ns = Ns Em count Ns | Ns Sy none Limits the number of filesystems and volumes that can exist under this point in the dataset tree. The limit is not enforced if the user is allowed to change the limit. Setting a .Sy filesystem_limit to .Sy on a descendent of a filesystem that already has a .Sy filesystem_limit does not override the ancestor's .Sy filesystem_limit , but rather imposes an additional limit. This feature must be enabled to be used .Po see .Xr zpool-features 5 .Pc . .It Sy special_small_blocks Ns = Ns Em size This value represents the threshold block size for including small file blocks into the special allocation class. Blocks smaller than or equal to this value will be assigned to the special allocation class while greater blocks will be assigned to the regular class. Valid values are zero or a power of two from 512B up to 1M. The default size is 0 which means no small file blocks will be allocated in the special class. .Pp Before setting this property, a special class vdev must be added to the pool. See .Xr zpoolconcepts 8 for more details on the special allocation class. .It Sy mountpoint Ns = Ns Pa path Ns | Ns Sy none Ns | Ns Sy legacy Controls the mount point used for this file system. See the .Em Mount Points section of .Xr zfsconcepts 8 for more information on how this property is used. .Pp When the .Sy mountpoint property is changed for a file system, the file system and any children that inherit the mount point are unmounted. If the new value is .Sy legacy , then they remain unmounted. Otherwise, they are automatically remounted in the new location if the property was previously .Sy legacy or .Sy none , or if they were mounted before the property was changed. In addition, any shared file systems are unshared and shared in the new location. .It Sy nbmand Ns = Ns Sy on Ns | Ns Sy off Controls whether the file system should be mounted with .Sy nbmand .Pq Non Blocking mandatory locks . This is used for SMB clients. Changes to this property only take effect when the file system is umounted and remounted. See .Xr mount 8 for more information on .Sy nbmand mounts. This property is not used on Linux. .It Sy overlay Ns = Ns Sy on Ns | Ns Sy off Allow mounting on a busy directory or a directory which already contains files or directories. This is the default mount behavior for Linux and FreeBSD file systems. On these platforms the property is .Sy on by default. Set to .Sy off to disable overlay mounts for consistency with OpenZFS on other platforms. .It Sy primarycache Ns = Ns Sy all Ns | Ns Sy none Ns | Ns Sy metadata Controls what is cached in the primary cache .Pq ARC . If this property is set to .Sy all , then both user data and metadata is cached. If this property is set to .Sy none , then neither user data nor metadata is cached. If this property is set to .Sy metadata , then only metadata is cached. The default value is .Sy all . .It Sy quota Ns = Ns Em size Ns | Ns Sy none Limits the amount of space a dataset and its descendents can consume. This property enforces a hard limit on the amount of space used. This includes all space consumed by descendents, including file systems and snapshots. Setting a quota on a descendent of a dataset that already has a quota does not override the ancestor's quota, but rather imposes an additional limit. .Pp Quotas cannot be set on volumes, as the .Sy volsize property acts as an implicit quota. .It Sy snapshot_limit Ns = Ns Em count Ns | Ns Sy none Limits the number of snapshots that can be created on a dataset and its descendents. Setting a .Sy snapshot_limit on a descendent of a dataset that already has a .Sy snapshot_limit does not override the ancestor's .Sy snapshot_limit , but rather imposes an additional limit. The limit is not enforced if the user is allowed to change the limit. For example, this means that recursive snapshots taken from the global zone are counted against each delegated dataset within a zone. This feature must be enabled to be used .Po see .Xr zpool-features 5 .Pc . .It Sy userquota@ Ns Em user Ns = Ns Em size Ns | Ns Sy none Limits the amount of space consumed by the specified user. User space consumption is identified by the .Sy userspace@ Ns Em user property. .Pp Enforcement of user quotas may be delayed by several seconds. This delay means that a user might exceed their quota before the system notices that they are over quota and begins to refuse additional writes with the .Er EDQUOT error message. See the .Nm zfs Cm userspace subcommand for more information. .Pp Unprivileged users can only access their own groups' space usage. The root user, or a user who has been granted the .Sy userquota privilege with .Nm zfs Cm allow , can get and set everyone's quota. .Pp This property is not available on volumes, on file systems before version 4, or on pools before version 15. The .Sy userquota@ Ns Em ... properties are not displayed by .Nm zfs Cm get Sy all . The user's name must be appended after the .Sy @ symbol, using one of the following forms: .Bl -bullet .It .Em POSIX name .Po for example, .Sy joe .Pc .It .Em POSIX numeric ID .Po for example, .Sy 789 .Pc .It .Em SID name .Po for example, .Sy joe.smith@mydomain .Pc .It .Em SID numeric ID .Po for example, .Sy S-1-123-456-789 .Pc .El .Pp Files created on Linux always have POSIX owners. .It Sy userobjquota@ Ns Em user Ns = Ns Em size Ns | Ns Sy none The .Sy userobjquota is similar to .Sy userquota but it limits the number of objects a user can create. Please refer to .Sy userobjused for more information about how objects are counted. .It Sy groupquota@ Ns Em group Ns = Ns Em size Ns | Ns Sy none Limits the amount of space consumed by the specified group. Group space consumption is identified by the .Sy groupused@ Ns Em group property. .Pp Unprivileged users can access only their own groups' space usage. The root user, or a user who has been granted the .Sy groupquota privilege with .Nm zfs Cm allow , can get and set all groups' quotas. .It Sy groupobjquota@ Ns Em group Ns = Ns Em size Ns | Ns Sy none The .Sy groupobjquota is similar to .Sy groupquota but it limits number of objects a group can consume. Please refer to .Sy userobjused for more information about how objects are counted. .It Sy projectquota@ Ns Em project Ns = Ns Em size Ns | Ns Sy none Limits the amount of space consumed by the specified project. Project space consumption is identified by the .Sy projectused@ Ns Em project property. Please refer to .Sy projectused for more information about how project is identified and set/changed. .Pp The root user, or a user who has been granted the .Sy projectquota privilege with .Nm zfs allow , can access all projects' quota. .It Sy projectobjquota@ Ns Em project Ns = Ns Em size Ns | Ns Sy none The .Sy projectobjquota is similar to .Sy projectquota but it limits number of objects a project can consume. Please refer to .Sy userobjused for more information about how objects are counted. .It Sy readonly Ns = Ns Sy on Ns | Ns Sy off Controls whether this dataset can be modified. The default value is .Sy off . The values .Sy on and .Sy off are equivalent to the .Sy ro and .Sy rw mount options. .Pp This property can also be referred to by its shortened column name, .Sy rdonly . .It Sy recordsize Ns = Ns Em size Specifies a suggested block size for files in the file system. This property is designed solely for use with database workloads that access files in fixed-size records. ZFS automatically tunes block sizes according to internal algorithms optimized for typical access patterns. .Pp For databases that create very large files but access them in small random chunks, these algorithms may be suboptimal. Specifying a .Sy recordsize greater than or equal to the record size of the database can result in significant performance gains. Use of this property for general purpose file systems is strongly discouraged, and may adversely affect performance. .Pp The size specified must be a power of two greater than or equal to 512 and less than or equal to 128 Kbytes. If the .Sy large_blocks feature is enabled on the pool, the size may be up to 1 Mbyte. See .Xr zpool-features 5 for details on ZFS feature flags. .Pp Changing the file system's .Sy recordsize affects only files created afterward; existing files are unaffected. .Pp This property can also be referred to by its shortened column name, .Sy recsize . .It Sy redundant_metadata Ns = Ns Sy all Ns | Ns Sy most Controls what types of metadata are stored redundantly. ZFS stores an extra copy of metadata, so that if a single block is corrupted, the amount of user data lost is limited. This extra copy is in addition to any redundancy provided at the pool level .Pq e.g. by mirroring or RAID-Z , and is in addition to an extra copy specified by the .Sy copies property .Pq up to a total of 3 copies . For example if the pool is mirrored, .Sy copies Ns = Ns 2 , and .Sy redundant_metadata Ns = Ns Sy most , then ZFS stores 6 copies of most metadata, and 4 copies of data and some metadata. .Pp When set to .Sy all , ZFS stores an extra copy of all metadata. If a single on-disk block is corrupt, at worst a single block of user data .Po which is .Sy recordsize bytes long .Pc can be lost. .Pp When set to .Sy most , ZFS stores an extra copy of most types of metadata. This can improve performance of random writes, because less metadata must be written. In practice, at worst about 100 blocks .Po of .Sy recordsize bytes each .Pc of user data can be lost if a single on-disk block is corrupt. The exact behavior of which metadata blocks are stored redundantly may change in future releases. .Pp The default value is .Sy all . .It Sy refquota Ns = Ns Em size Ns | Ns Sy none Limits the amount of space a dataset can consume. This property enforces a hard limit on the amount of space used. This hard limit does not include space used by descendents, including file systems and snapshots. .It Sy refreservation Ns = Ns Em size Ns | Ns Sy none Ns | Ns Sy auto The minimum amount of space guaranteed to a dataset, not including its descendents. When the amount of space used is below this value, the dataset is treated as if it were taking up the amount of space specified by .Sy refreservation . The .Sy refreservation reservation is accounted for in the parent datasets' space used, and counts against the parent datasets' quotas and reservations. .Pp If .Sy refreservation is set, a snapshot is only allowed if there is enough free pool space outside of this reservation to accommodate the current number of .Qq referenced bytes in the dataset. .Pp If .Sy refreservation is set to .Sy auto , a volume is thick provisioned .Po or .Qq not sparse .Pc . .Sy refreservation Ns = Ns Sy auto is only supported on volumes. See .Sy volsize in the .Sx Native Properties section for more information about sparse volumes. .Pp This property can also be referred to by its shortened column name, .Sy refreserv . .It Sy relatime Ns = Ns Sy on Ns | Ns Sy off Controls the manner in which the access time is updated when .Sy atime=on is set. Turning this property on causes the access time to be updated relative to the modify or change time. Access time is only updated if the previous access time was earlier than the current modify or change time or if the existing access time hasn't been updated within the past 24 hours. The default value is .Sy off . The values .Sy on and .Sy off are equivalent to the .Sy relatime and .Sy norelatime mount options. .It Sy reservation Ns = Ns Em size Ns | Ns Sy none The minimum amount of space guaranteed to a dataset and its descendants. When the amount of space used is below this value, the dataset is treated as if it were taking up the amount of space specified by its reservation. Reservations are accounted for in the parent datasets' space used, and count against the parent datasets' quotas and reservations. .Pp This property can also be referred to by its shortened column name, .Sy reserv . .It Sy secondarycache Ns = Ns Sy all Ns | Ns Sy none Ns | Ns Sy metadata Controls what is cached in the secondary cache .Pq L2ARC . If this property is set to .Sy all , then both user data and metadata is cached. If this property is set to .Sy none , then neither user data nor metadata is cached. If this property is set to .Sy metadata , then only metadata is cached. The default value is .Sy all . .It Sy setuid Ns = Ns Sy on Ns | Ns Sy off Controls whether the setuid bit is respected for the file system. The default value is .Sy on . The values .Sy on and .Sy off are equivalent to the .Sy suid and .Sy nosuid mount options. .It Sy sharesmb Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Em opts Controls whether the file system is shared by using .Sy Samba USERSHARES and what options are to be used. Otherwise, the file system is automatically shared and unshared with the .Nm zfs Cm share and .Nm zfs Cm unshare commands. If the property is set to on, the .Xr net 8 command is invoked to create a .Sy USERSHARE . .Pp Because SMB shares requires a resource name, a unique resource name is constructed from the dataset name. The constructed name is a copy of the dataset name except that the characters in the dataset name, which would be invalid in the resource name, are replaced with underscore (_) characters. Linux does not currently support additional options which might be available on Solaris. .Pp If the .Sy sharesmb property is set to .Sy off , the file systems are unshared. .Pp The share is created with the ACL (Access Control List) "Everyone:F" ("F" stands for "full permissions", ie. read and write permissions) and no guest access (which means Samba must be able to authenticate a real user, system passwd/shadow, LDAP or smbpasswd based) by default. This means that any additional access control (disallow specific user specific access etc) must be done on the underlying file system. .It Sy sharenfs Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Em opts Controls whether the file system is shared via NFS, and what options are to be used. A file system with a .Sy sharenfs property of .Sy off is managed with the .Xr exportfs 8 command and entries in the .Em /etc/exports file. Otherwise, the file system is automatically shared and unshared with the .Nm zfs Cm share and .Nm zfs Cm unshare commands. If the property is set to .Sy on , the dataset is shared using the default options: .Pp .Em sec=sys,rw,crossmnt,no_subtree_check .Pp See .Xr exports 5 for the meaning of the default options. Otherwise, the .Xr exportfs 8 command is invoked with options equivalent to the contents of this property. .Pp When the .Sy sharenfs property is changed for a dataset, the dataset and any children inheriting the property are re-shared with the new options, only if the property was previously .Sy off , or if they were shared before the property was changed. If the new property is .Sy off , the file systems are unshared. .It Sy logbias Ns = Ns Sy latency Ns | Ns Sy throughput Provide a hint to ZFS about handling of synchronous requests in this dataset. If .Sy logbias is set to .Sy latency .Pq the default , ZFS will use pool log devices .Pq if configured to handle the requests at low latency. If .Sy logbias is set to .Sy throughput , ZFS will not use configured pool log devices. ZFS will instead optimize synchronous operations for global pool throughput and efficient use of resources. .It Sy snapdev Ns = Ns Sy hidden Ns | Ns Sy visible Controls whether the volume snapshot devices under .Em /dev/zvol/ are hidden or visible. The default value is .Sy hidden . .It Sy snapdir Ns = Ns Sy hidden Ns | Ns Sy visible Controls whether the .Pa .zfs directory is hidden or visible in the root of the file system as discussed in the .Em Snapshots section of .Xr zfsconcepts 8 . The default value is .Sy hidden . .It Sy sync Ns = Ns Sy standard Ns | Ns Sy always Ns | Ns Sy disabled Controls the behavior of synchronous requests .Pq e.g. fsync, O_DSYNC . .Sy standard is the .Tn POSIX specified behavior of ensuring all synchronous requests are written to stable storage and all devices are flushed to ensure data is not cached by device controllers .Pq this is the default . .Sy always causes every file system transaction to be written and flushed before its system call returns. This has a large performance penalty. .Sy disabled disables synchronous requests. File system transactions are only committed to stable storage periodically. This option will give the highest performance. However, it is very dangerous as ZFS would be ignoring the synchronous transaction demands of applications such as databases or NFS. Administrators should only use this option when the risks are understood. .It Sy version Ns = Ns Em N Ns | Ns Sy current The on-disk version of this file system, which is independent of the pool version. This property can only be set to later supported versions. See the .Nm zfs Cm upgrade command. .It Sy volsize Ns = Ns Em size For volumes, specifies the logical size of the volume. By default, creating a volume establishes a reservation of equal size. For storage pools with a version number of 9 or higher, a .Sy refreservation is set instead. Any changes to .Sy volsize are reflected in an equivalent change to the reservation .Po or .Sy refreservation .Pc . The .Sy volsize can only be set to a multiple of .Sy volblocksize , and cannot be zero. .Pp The reservation is kept equal to the volume's logical size to prevent unexpected behavior for consumers. Without the reservation, the volume could run out of space, resulting in undefined behavior or data corruption, depending on how the volume is used. These effects can also occur when the volume size is changed while it is in use .Pq particularly when shrinking the size . Extreme care should be used when adjusting the volume size. .Pp Though not recommended, a .Qq sparse volume .Po also known as .Qq thin provisioned .Pc can be created by specifying the .Fl s option to the .Nm zfs Cm create Fl V command, or by changing the value of the .Sy refreservation property .Po or .Sy reservation property on pool version 8 or earlier .Pc after the volume has been created. A .Qq sparse volume is a volume where the value of .Sy refreservation is less than the size of the volume plus the space required to store its metadata. Consequently, writes to a sparse volume can fail with .Er ENOSPC when the pool is low on space. For a sparse volume, changes to .Sy volsize are not reflected in the .Sy refreservation. A volume that is not sparse is said to be .Qq thick provisioned . A sparse volume can become thick provisioned by setting .Sy refreservation to .Sy auto . .It Sy volmode Ns = Ns Cm default | full | geom | dev | none This property specifies how volumes should be exposed to the OS. Setting it to .Sy full exposes volumes as fully fledged block devices, providing maximal functionality. The value .Sy geom is just an alias for .Sy full and is kept for compatibility. Setting it to .Sy dev hides its partitions. Volumes with property set to .Sy none are not exposed outside ZFS, but can be snapshotted, cloned, replicated, etc, that can be suitable for backup purposes. Value .Sy default means that volumes exposition is controlled by system-wide tunable .Va zvol_volmode , where .Sy full , .Sy dev and .Sy none are encoded as 1, 2 and 3 respectively. The default value is .Sy full . .It Sy vscan Ns = Ns Sy on Ns | Ns Sy off Controls whether regular files should be scanned for viruses when a file is opened and closed. In addition to enabling this property, the virus scan service must also be enabled for virus scanning to occur. The default value is .Sy off . This property is not used on Linux. .It Sy xattr Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Sy sa Controls whether extended attributes are enabled for this file system. Two styles of extended attributes are supported either directory based or system attribute based. .Pp The default value of .Sy on enables directory based extended attributes. This style of extended attribute imposes no practical limit on either the size or number of attributes which can be set on a file. Although under Linux the .Xr getxattr 2 and .Xr setxattr 2 system calls limit the maximum size to 64K. This is the most compatible style of extended attribute and is supported by all OpenZFS implementations. .Pp System attribute based xattrs can be enabled by setting the value to .Sy sa . The key advantage of this type of xattr is improved performance. Storing extended attributes as system attributes significantly decreases the amount of disk IO required. Up to 64K of data may be stored per-file in the space reserved for system attributes. If there is not enough space available for an extended attribute then it will be automatically written as a directory based xattr. System attribute based extended attributes are not accessible on platforms which do not support the .Sy xattr=sa feature. .Pp The use of system attribute based xattrs is strongly encouraged for users of SELinux or POSIX ACLs. Both of these features heavily rely on extended attributes and benefit significantly from the reduced access time. .Pp The values .Sy on and .Sy off are equivalent to the .Sy xattr and .Sy noxattr mount options. .It Sy jailed Ns = Ns Sy off Ns | Ns Sy on Controls whether the dataset is managed from a jail. See the .Qq Sx Jails section in .Xr zfs 8 for more information. Jails are a FreeBSD feature and are not relevant on other platforms. The default value is .Cm off . .It Sy zoned Ns = Ns Sy on Ns | Ns Sy off Controls whether the dataset is managed from a non-global zone. Zones are a Solaris feature and are not relevant on other platforms. The default value is .Sy off . .El .Pp The following three properties cannot be changed after the file system is created, and therefore, should be set when the file system is created. If the properties are not set with the .Nm zfs Cm create or .Nm zpool Cm create commands, these properties are inherited from the parent dataset. If the parent dataset lacks these properties due to having been created prior to these features being supported, the new file system will have the default values for these properties. .Bl -tag -width "" .It Xo .Sy casesensitivity Ns = Ns Sy sensitive Ns | Ns .Sy insensitive Ns | Ns Sy mixed .Xc Indicates whether the file name matching algorithm used by the file system should be case-sensitive, case-insensitive, or allow a combination of both styles of matching. The default value for the .Sy casesensitivity property is .Sy sensitive . Traditionally, .Ux and .Tn POSIX file systems have case-sensitive file names. .Pp The .Sy mixed value for the .Sy casesensitivity property indicates that the file system can support requests for both case-sensitive and case-insensitive matching behavior. Currently, case-insensitive matching behavior on a file system that supports mixed behavior is limited to the SMB server product. For more information about the .Sy mixed value behavior, see the "ZFS Administration Guide". .It Xo .Sy normalization Ns = Ns Sy none Ns | Ns Sy formC Ns | Ns .Sy formD Ns | Ns Sy formKC Ns | Ns Sy formKD .Xc Indicates whether the file system should perform a .Sy unicode normalization of file names whenever two file names are compared, and which normalization algorithm should be used. File names are always stored unmodified, names are normalized as part of any comparison process. If this property is set to a legal value other than .Sy none , and the .Sy utf8only property was left unspecified, the .Sy utf8only property is automatically set to .Sy on . The default value of the .Sy normalization property is .Sy none . This property cannot be changed after the file system is created. .It Sy utf8only Ns = Ns Sy on Ns | Ns Sy off Indicates whether the file system should reject file names that include characters that are not present in the .Sy UTF-8 character code set. If this property is explicitly set to .Sy off , the normalization property must either not be explicitly set or be set to .Sy none . The default value for the .Sy utf8only property is .Sy off . This property cannot be changed after the file system is created. .El .Pp The .Sy casesensitivity , .Sy normalization , and .Sy utf8only properties are also new permissions that can be assigned to non-privileged users by using the ZFS delegated administration feature. .Ss "Temporary Mount Point Properties" When a file system is mounted, either through .Xr mount 8 for legacy mounts or the .Nm zfs Cm mount command for normal file systems, its mount options are set according to its properties. The correlation between properties and mount options is as follows: .Bd -literal PROPERTY MOUNT OPTION atime atime/noatime canmount auto/noauto devices dev/nodev exec exec/noexec readonly ro/rw relatime relatime/norelatime setuid suid/nosuid xattr xattr/noxattr .Ed .Pp In addition, these options can be set on a per-mount basis using the .Fl o option, without affecting the property that is stored on disk. The values specified on the command line override the values stored in the dataset. The .Sy nosuid option is an alias for .Sy nodevices Ns \&, Ns Sy nosetuid . These properties are reported as .Qq temporary by the .Nm zfs Cm get command. If the properties are changed while the dataset is mounted, the new setting overrides any temporary settings. .Ss "User Properties" In addition to the standard native properties, ZFS supports arbitrary user properties. User properties have no effect on ZFS behavior, but applications or administrators can use them to annotate datasets .Pq file systems, volumes, and snapshots . .Pp User property names must contain a colon .Pq Qq Sy \&: character to distinguish them from native properties. They may contain lowercase letters, numbers, and the following punctuation characters: colon .Pq Qq Sy \&: , dash .Pq Qq Sy - , period .Pq Qq Sy \&. , and underscore .Pq Qq Sy _ . The expected convention is that the property name is divided into two portions such as .Em module Ns \&: Ns Em property , but this namespace is not enforced by ZFS. User property names can be at most 256 characters, and cannot begin with a dash .Pq Qq Sy - . .Pp When making programmatic use of user properties, it is strongly suggested to use a reversed .Sy DNS domain name for the .Em module component of property names to reduce the chance that two independently-developed packages use the same property name for different purposes. .Pp The values of user properties are arbitrary strings, are always inherited, and are never validated. All of the commands that operate on properties .Po Nm zfs Cm list , .Nm zfs Cm get , .Nm zfs Cm set , and so forth .Pc can be used to manipulate both native properties and user properties. Use the .Nm zfs Cm inherit command to clear a user property. If the property is not defined in any parent dataset, it is removed entirely. Property values are limited to 8192 bytes.