NAME¶
rbd - manage rados block device (RBD) images
SYNOPSIS¶
rbd [ -c ceph.conf ] [ -m monaddr ] [ -p | --pool pool ] [
--size size ] [ --order bits ] [ command ... ]
DESCRIPTION¶
rbd is a utility for manipulating rados block device (RBD) images, used
by the Linux rbd driver and the rbd storage driver for Qemu/KVM. RBD images
are simple block devices that are striped over objects and stored in a RADOS
object store. The size of the objects the image is striped over must be a
power of two.
OPTIONS¶
- -c ceph.conf, --conf ceph.conf
- Use ceph.conf configuration file instead of the default
/etc/ceph/ceph.conf to determine monitor addresses during startup.
- -m monaddress[:port]
- Connect to specified monitor (instead of looking through
ceph.conf).
- -p pool, --pool pool
- Interact with the given pool. Required by most
commands.
- --no-progress
- Do not output progress information (goes to standard error
by default for some commands).
PARAMETERS¶
- --image-format format
- Specifies which object layout to use. The default is
1.
- •
- format 1 - Use the original format for a new rbd image.
This format is understood by all versions of librbd and the kernel rbd
module, but does not support newer features like cloning.
- •
- format 2 - Use the second rbd format, which is supported by
librbd (but not the kernel rbd module) at this time. This adds support for
cloning and is more easily extensible to allow more features in the
future.
- --size size-in-mb
- Specifies the size (in megabytes) of the new rbd
image.
- --order bits
- Specifies the object size expressed as a number of bits,
such that the object size is 1 << order. The default is 22 (4
MB).
- --stripe-unit size-in-bytes
- Specifies the stripe unit size in bytes. See striping
section (below) for more details.
- --stripe-count num
- Specifies the number of objects to stripe over before
looping back to the first object. See striping section (below) for more
details.
- --snap snap
- Specifies the snapshot name for the specific
operation.
- --id username
- Specifies the username (without the client. prefix)
to use with the map command.
- --keyfile filename
- Specifies a file containing the secret to use with the map
command. If not specified, client.admin will be used by
default.
- --keyring filename
- Specifies a keyring file containing a secret for the
specified user to use with the map command. If not specified, the default
keyring locations will be searched.
- --shared tag
- Option for lock add that allows multiple clients to
lock the same image if they use the same tag. The tag is an arbitrary
string. This is useful for situations where an image must be open from
more than one client at once, like during live migration of a virtual
machine, or for use underneath a clustered filesystem.
- --format format
- Specifies output formatting (default: plain, json,
xml)
- --pretty-format
- Make json or xml formatted output more human-readable.
- -o map-options, --options map-options
- Specifies which options to use when mapping an image.
map-options is a comma-separated string of options (similar to mount(8)
mount options). See map options section below for more details.
- --read-only
- Map the image read-only. Equivalent to -o ro.
COMMANDS¶
- ls [-l | --long] [pool-name]
- Will list all rbd images listed in the rbd_directory
object. With -l, also show snapshots, and use longer-format output
including size, parent (if clone), format, etc.
- info [image-name]
- Will dump information (such as size and order) about a
specific rbd image. If image is a clone, information about its parent is
also displayed. If a snapshot is specified, whether it is protected is
shown as well.
- create [image-name]
- Will create a new rbd image. You must also specify the size
via --size. The --stripe-unit and --stripe-count arguments are optional,
but must be used together.
- clone [parent-snapname]
[image-name]
- Will create a clone (copy-on-write child) of the parent
snapshot. Object order will be identical to that of the parent image
unless specified. Size will be the same as the parent snapshot.
The parent snapshot must be protected (see rbd snap protect). This
requires image format 2.
- flatten [image-name]
- If image is a clone, copy all shared blocks from the parent
snapshot and make the child independent of the parent, severing the link
between parent snap and child. The parent snapshot can be unprotected and
deleted if it has no further dependent clones.
This requires image format 2.
- children [image-name]
- List the clones of the image at the given snapshot. This
checks every pool, and outputs the resulting poolname/imagename.
This requires image format 2.
- resize [image-name]
[--allow-shrink]
- Resizes rbd image. The size parameter also needs to be
specified. The --allow-shrink option lets the size be reduced.
- rm [image-name]
- Deletes an rbd image (including all data blocks). If the
image has snapshots, this fails and nothing is deleted.
- export [image-name]
[dest-path]
- Exports image to dest path (use - for stdout).
- import [path] [dest-image]
- Creates a new image and imports its data from path (use -
for stdin). The import operation will try to create sparse rbd images if
possible. For import from stdin, the sparsification unit is the data block
size of the destination image (1 << order).
- export-diff [image-name]
[dest-path] [--from-snap snapname]
- Exports an incremental diff for an image to dest path (use
- for stdout). If an initial snapshot is specified, only changes since
that snapshot are included; otherwise, any regions of the image that
contain data are included. The end snapshot is specified using the
standard --snap option or @snap syntax (see below). The image diff format
includes metadata about image size changes, and the start and end
snapshots. It efficiently represents discarded or 'zero' regions of the
image.
- import-diff [src-path]
[image-name]
- Imports an incremental diff of an image and applies it to
the current image. If the diff was generated relative to a start snapshot,
we verify that snapshot already exists before continuing. If there was an
end snapshot we verify it does not already exist before applying the
changes, and create the snapshot when we are done.
- diff [image-name] [--from-snap
snapname]
- Dump a list of byte extents in the image that have changed
since the specified start snapshot, or since the image was created. Each
output line includes the starting offset (in bytes), the length of the
region (in bytes), and either 'zero' or 'data' to indicate whether the
region is known to be zeros or may contain other data.
- cp [src-image]
[dest-image]
- Copies the content of a src-image into the newly created
dest-image. dest-image will have the same size, order, and image format as
src-image.
- mv [src-image]
[dest-image]
- Renames an image. Note: rename across pools is not
supported.
- snap ls [image-name]
- Dumps the list of snapshots inside a specific image.
- snap create [image-name]
- Creates a new snapshot. Requires the snapshot name
parameter specified.
- snap rollback [image-name]
- Rollback image content to snapshot. This will iterate
through the entire blocks array and update the data head content to the
snapshotted version.
- snap rm [image-name]
- Removes the specified snapshot.
- snap purge [image-name]
- Removes all snapshots from an image.
- snap protect [image-name]
- Protect a snapshot from deletion, so that clones can be
made of it (see rbd clone). Snapshots must be protected before
clones are made; protection implies that there exist dependent cloned
children that refer to this snapshot. rbd clone will fail on a
nonprotected snapshot.
This requires image format 2.
- snap unprotect [image-name]
- Unprotect a snapshot from deletion (undo snap
protect). If cloned children remain, snap unprotect fails.
(Note that clones may exist in different pools than the parent snapshot.)
This requires image format 2.
- map [image-name] [-o | --options
map-options ] [--read-only]
- Maps the specified image to a block device via the rbd
kernel module.
- unmap [device-path]
- Unmaps the block device that was mapped via the rbd kernel
module.
- showmapped
- Show the rbd images that are mapped via the rbd kernel
module.
- lock list [image-name]
- Show locks held on the image. The first column is the
locker to use with the lock remove command.
- lock add [image-name]
[lock-id]
- Lock an image. The lock-id is an arbitrary name for the
user's convenience. By default, this is an exclusive lock, meaning it will
fail if the image is already locked. The --shared option changes this
behavior. Note that locking does not affect any operation other than
adding a lock. It does not protect an image from being deleted.
- lock remove [image-name] [lock-id]
[ locker]
- Release a lock on an image. The lock id and locker are as
output by lock ls.
- bench-write [image-name] --io-size
[io-size-in-bytes] --io-threads [ num-ios-in-flight]
--io-total [ total-bytes-to-write]
- Generate a series of sequential writes to the image and
measure the write throughput and latency. Defaults are: --io-size 4096,
--io-threads 16, --io-total 1GB
IMAGE NAME¶
In addition to using the --pool and the --snap options, the image name can
include both the pool name and the snapshot name. The image name format is as
follows:
Thus an image name that contains a slash character ('/') requires specifying the
pool name explicitly.
STRIPING¶
RBD images are striped over many objects, which are then stored by the Ceph
distributed object store (RADOS). As a result, read and write requests for the
image are distributed across many nodes in the cluster, generally preventing
any single node from becoming a bottleneck when individual images get large or
busy.
The striping is controlled by three parameters:
- order
- The size of objects we stripe over is a power of two,
specifially 2^[*order*] bytes. The default
- is 22, or 4 MB.
- stripe_unit
- Each [*stripe_unit*] contiguous bytes are stored
adjacently in the same object, before we move on
- to the next object.
- stripe_count
- After we write [*stripe_unit*] bytes to [*stripe_count*]
objects, we loop back to the initial object
- and write another stripe, until the object reaches its
maximum size (as specified by [*order*]. At that
- point, we move on to the next [*stripe_count*]
objects.
By default, [
stripe_unit] is the same as the object size and
[
stripe_count] is 1. Specifying a different [
stripe_unit]
requires that the STRIPINGV2 feature be supported (added in Ceph v0.53) and
format 2 images be used.
MAP OPTIONS¶
Most of these options are useful mainly for debugging and benchmarking. The
default values are set in the kernel and may therefore depend on the version
of the running kernel.
- •
- fsid=aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee - FSID that
should be assumed by the client.
- •
- ip=a.b.c.d[:p] - IP and, optionally, port the client should
use.
- •
- share - Enable sharing of client instances with other
mappings (default).
- •
- noshare - Disable sharing of client instances with other
mappings.
- •
- crc - Enable CRC32C checksumming for data writes
(default).
- •
- nocrc - Disable CRC32C checksumming for data writes.
- •
- osdkeepalive=x - OSD keepalive timeout (default is 5
seconds).
- •
- osd_idle_ttl=x - OSD idle TTL (default is 60 seconds).
- •
- rw - Map the image read-write (default).
- •
- ro - Map the image read-only. Equivalent to
--read-only.
EXAMPLES¶
To create a new rbd image that is 100 GB:
rbd -p mypool create myimage --size 102400
or alternatively:
rbd create mypool/myimage --size 102400
To use a non-default object size (8 MB):
rbd create mypool/myimage --size 102400 --order 23
To delete an rbd image (be careful!):
To create a new snapshot:
rbd snap create mypool/myimage@mysnap
To create a copy-on-write clone of a protected snapshot:
rbd clone mypool/myimage@mysnap otherpool/cloneimage
To see which clones of a snapshot exist:
rbd children mypool/myimage@mysnap
To delete a snapshot:
rbd snap rm mypool/myimage@mysnap
To map an image via the kernel with cephx enabled:
rbd map mypool/myimage --id admin --keyfile secretfile
To unmap an image:
To create an image and a clone from it:
rbd import --image-format 2 image mypool/parent
rbd snap create --snap snapname mypool/parent
rbd snap protect mypool/parent@snap
rbd clone mypool/parent@snap otherpool/child
To create an image with a smaller stripe_unit (to better distribute small writes
in some workloads):
rbd -p mypool create myimage --size 102400 --stripe-unit 65536 --stripe-count 16
To change an image from one image format to another, export it and then import
it as the desired image format:
rbd export mypool/myimage@snap /tmp/img
rbd import --image-format 2 /tmp/img mypool/myimage2
To lock an image for exclusive use:
rbd lock add mypool/myimage mylockid
To release a lock:
rbd lock remove mypool/myimage mylockid client.2485
AVAILABILITY¶
rbd is part of the Ceph distributed storage system. Please refer to the
Ceph documentation at
http://ceph.com/docs for more information.
SEE ALSO¶
ceph(8),
rados(8)
COPYRIGHT¶
2010-2014, Inktank Storage, Inc. and contributors. Licensed under Creative
Commons BY-SA