NAME¶mkfs.btrfs - create a btrfs filesystem
SYNOPSIS¶mkfs.btrfs [-A|--alloc-start <alloc-start>] [-b|--byte-count <byte-count>] [-d|--data <data-profile>] [-m|--metadata <metadata profile>] [-M|--mixed] [-l|--leafsize <leafsize>] [-n|--nodesize <nodesize>] [-s|--sectorsize <sectorsize>] [-L|--label <label>] [-K|--nodiscard] [-r|--rootdir <rootdir>] [-O|--features <feature1>[,<feature2>...]] [-U|--uuid <UUID>] [-f|--force] [-q|--quiet] [--help] [-V|--version] <device> [<device>...]
DESCRIPTION¶mkfs.btrfs is used to create the btrfs filesystem on a single or multiple devices. <device> is typically a block device but can be a file-backed image as well. Multiple devices are grouped by UUID of the filesystem.
(An option to help debugging chunk allocator.) Specify the (physical) offset from the start of the device at which allocations start. The default value is zero.-b|--byte-count <size>
Specify the size of the filesystem. If this option is not used, mkfs.btrfs uses the entire device space for the filesystem.-d|--data <profile>
Specify the profile for the data block groups. Valid values are raid0, raid1, raid5, raid6, raid10 or single or dup (case does not matter).See DUP PROFILES ON A SINGLE DEVICE for more.-m|--metadata <profile>
Specify the profile for the metadata block groups. Valid values are raid0, raid1, raid5, raid6, raid10, single or dup, (case does not matter).A single device filesystem will default to DUP, unless a SSD is detected. Then it will default to single. The detection is based on the value of /sys/block/DEV/queue/rotational, where DEV is the short name of the device.Note that the rotational status can be arbitrarily set by the underlying block device driver and may not reflect the true status (network block device, memory-backed SCSI devices etc). Use the options --data/--metadata to avoid confusion.See DUP PROFILES ON A SINGLE DEVICE for more details.-M|--mixed
Normally the data and metadata block groups are isolated. The mixed mode will remove the isolation and store both types in the same block group type. This helps to utilize the free space regardless of the purpose and is suitable for small devices. The separate allocation of block groups leads to a situation where the space is reserved for the other block group type, is not available for allocation and can lead to ENOSPC state.The recommended size for the mixed mode is for filesystems less than 1GiB. The soft recommendation is to use it for filesystems smaller than 5GiB. The mixed mode may lead to degraded performance on larger filesystems, but is otherwise usable, even on multiple devices.The nodesize and sectorsize must be equal, and the block group types must match.Noteversions up to 4.2.x forced the mixed mode for devices smaller than 1GiB. This has been removed in 4.3+ as it caused some usability issues.-l|--leafsize <size>
Alias for --nodesize. Deprecated.-n|--nodesize <size>
Specify the nodesize, the tree block size in which btrfs stores metadata. The default value is 16KiB (16384) or the page size, whichever is bigger. Must be a multiple of the sectorsize, but not larger than 64KiB (65536). Leafsize always equals nodesize and the options are aliases.Smaller node size increases fragmentation but lead to higher b-trees which in turn leads to lower locking contention. Higher node sizes give better packing and less fragmentation at the cost of more expensive memory operations while updating the metadata blocks.Noteversions up to 3.11 set the nodesize to 4k.-s|--sectorsize <size>
Specify the sectorsize, the minimum data block allocation unit.The default value is the page size and is autodetected. If the sectorsize differs from the page size, the created filesystem may not be mountable by the kernel. Therefore it is not recommended to use this option unless you are going to mount it on a system with the appropriate page size.-L|--label <string>
Specify a label for the filesystem. The string should be less than 256 bytes and must not contain newline characters.-K|--nodiscard
Do not perform whole device TRIM operation on devices that are capable of that.-r|--rootdir <rootdir>
Populate the toplevel subvolume with files from rootdir. This does not require root permissions and does not mount the filesystem.-O|--features <feature1>[,<feature2> ...]
A list of filesystem features turned on at mkfs time. Not all features are supported by old kernels. To disable a feature, prefix it with ^.See section FILESYSTEM FEATURES for more details. To see all available features that mkfs.btrfs supports run:mkfs.btrfs -O list-all-f|--force
Forcibly overwrite the block devices when an existing filesystem is detected. By default, mkfs.btrfs will utilize libblkid to check for any known filesystem on the devices. Alternatively you can use the wipefs utility to clear the devices.-q|--quiet
Print only error or warning messages. Options --features or --help are unaffected.-U|--uuid <UUID>
Create the filesystem with the given UUID. The UUID must not exist on any filesystem currently present.-V|--version
Print the mkfs.btrfs version and exit.--help
SIZE UNITS¶The default unit is byte. All size parameters accept suffixes in the 1024 base. The recognized suffixes are: k, m, g, t, p, e, both uppercase and lowercase.
MULTIPLE DEVICES¶Before mounting a multiple device filesystem, the kernel module must know the association of the block devices that are attached to the filesystem UUID.
# mount -o device=/dev/sdb,device=/dev/sdc /dev/sda /mnt
FILESYSTEM FEATURES¶Features that can be enabled during creation time. See also btrfs(5) section FILESYSTEM FEATURES. mixed-bg
(kernel support since 2.6.37)mixed data and metadata block groups, also set by option --mixedextref
(default since btrfs-progs 3.12, kernel support since 3.7)increased hardlink limit per file in a directory to 65536, older kernels supported a varying number of hardlinks depending on the sum of all file name sizes that can be stored into one metadata blockraid56
(kernel support since 3.9)extended format for RAID5/6, also enabled if raid5 or raid6 block groups are selectedskinny-metadata
(default since btrfs-progs 3.18, kernel support since 3.10)reduced-size metadata for extent references, saves a few percent of metadatano-holes
(kernel support since 3.14)improved representation of file extents where holes are not explicitly stored as an extent, saves a few percent of metadata if sparse files are used
BLOCK GROUPS, CHUNKS, RAID¶The highlevel organizational units of a filesystem are block groups of three types: data, metadata and system. DATA
store data blocks and nothing elseMETADATA
store internal metadata in b-trees, can store file data if they fit into the inline limitSYSTEM
store structures that describe the mapping between the physical devices and the linear logical space representing the filesystem
a logical range of space of a given profile, stores data, metadata or both; sometimes the terms are used interchangeablyA typical size of metadata block group is 256MiB (filesystem smaller than 50GiB) and 1GiB (larger than 50GiB), for data it’s 1GiB. The system block group size is a few megabytes.RAID
a block group profile type that utilizes RAID-like features on multiple devices: striping, mirroring, parityprofile
when used in connection with block groups refers to the allocation strategy and constraints, see the section PROFILES for more details
PROFILES¶There are the following block group types available:
|DUP||2 / 1 device||1/any (see note 1)|
|RAID0||1 to N||2/any|
|RAID10||2||1 to N||4/any|
|RAID5||1||1||2 to N - 1||2/any (see note 2)|
|RAID6||1||2||3 to N - 2||3/any (see note 3)|
DUP PROFILES ON A SINGLE DEVICE¶The mkfs utility will let the user create a filesystem with profiles that write the logical blocks to 2 physical locations. Whether there are really 2 physical copies highly depends on the underlying device type.
KNOWN ISSUES¶SMALL FILESYSTEMS AND LARGE NODESIZE
# mkfs.btrfs -f -n 65536 /dev/loop0 btrfs-progs v3.19-rc2-405-g976307c See http://btrfs.wiki.kernel.org for more information.
Performing full device TRIM (512.00MiB) ... Label: (null) UUID: 49fab72e-0c8b-466b-a3ca-d1bfe56475f0 Node size: 65536 Sector size: 4096 Filesystem size: 512.00MiB Block group profiles: Data: single 8.00MiB Metadata: DUP 40.00MiB System: DUP 12.00MiB SSD detected: no Incompat features: extref, skinny-metadata Number of devices: 1 Devices: ID SIZE PATH 1 512.00MiB /dev/loop0
# mount /dev/loop0 /mnt/ mount: mount /dev/loop0 on /mnt failed: No space left on device
AVAILABILITY¶mkfs.btrfs is part of btrfs-progs. Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for further details.
SEE ALSO¶btrfs(5), btrfs(8), wipefs(8)