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374 lines
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ReStructuredText
374 lines
12 KiB
ReStructuredText
===============================================
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rbd -- manage rados block device (RBD) images
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===============================================
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.. program:: rbd
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Synopsis
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========
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| **rbd** [ -c *ceph.conf* ] [ -m *monaddr* ] [ -p | --pool *pool* ] [
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--size *size* ] [ --order *bits* ] [ *command* ... ]
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Description
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===========
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**rbd** is a utility for manipulating rados block device (RBD) images,
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used by the Linux rbd driver and the rbd storage driver for Qemu/KVM.
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RBD images are simple block devices that are striped over objects and
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stored in a RADOS object store. The size of the objects the image is
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striped over must be a power of two.
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Options
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=======
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.. option:: -c ceph.conf, --conf ceph.conf
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Use ceph.conf configuration file instead of the default /etc/ceph/ceph.conf to
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determine monitor addresses during startup.
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.. option:: -m monaddress[:port]
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Connect to specified monitor (instead of looking through ceph.conf).
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.. option:: -p pool, --pool pool
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Interact with the given pool. Required by most commands.
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Parameters
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==========
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.. option:: --image-format format
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Specifies which object layout to use. The default is 1.
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* format 1 - Use the original format for a new rbd image. This format is
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understood by all versions of librbd and the kernel rbd module, but
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does not support newer features like cloning.
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* format 2 - Use the second rbd format, which is supported by
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librbd (but not the kernel rbd module) at this time. This adds
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support for cloning and is more easily extensible to allow more
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features in the future.
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.. option:: --size size-in-mb
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Specifies the size (in megabytes) of the new rbd image.
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.. option:: --order bits
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Specifies the object size expressed as a number of bits, such that
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the object size is ``1 << order``. The default is 22 (4 MB).
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.. option:: --stripe-unit size-in-bytes
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Specifies the stripe unit size in bytes. See striping section (below) for more details.
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.. option:: --stripe-count num
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Specifies the number of objects to stripe over before looping back
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to the first object. See striping section (below) for more details.
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.. option:: --snap snap
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Specifies the snapshot name for the specific operation.
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.. option:: --id username
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Specifies the username (without the ``client.`` prefix) to use with the map command.
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.. option:: --keyfile filename
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Specifies a file containing the secret to use with the map command.
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If not specified, ``client.admin`` will be used by default.
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.. option:: --keyring filename
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Specifies a keyring file containing a secret for the specified user
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to use with the map command. If not specified, the default keyring
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locations will be searched.
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.. option:: --shared tag
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Option for `lock add` that allows multiple clients to lock the
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same image if they use the same tag. The tag is an arbitrary
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string. This is useful for situations where an image must
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be open from more than one client at once, like during
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live migration of a virtual machine, or for use underneath
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a clustered filesystem.
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.. option:: --format format
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Specifies output formatting (default: plain, json, xml)
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.. option:: --pretty-format
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Make json or xml formatted output more human-readable.
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Commands
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========
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.. TODO rst "option" directive seems to require --foo style options, parsing breaks on subcommands.. the args show up as bold too
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:command:`ls` [-l | --long] [pool-name]
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Will list all rbd images listed in the rbd_directory object. With
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-l, also show snapshots, and use longer-format output including
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size, parent (if clone), format, etc.
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:command:`info` [*image-name*]
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Will dump information (such as size and order) about a specific rbd image.
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If image is a clone, information about its parent is also displayed.
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If a snapshot is specified, whether it is protected is shown as well.
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:command:`create` [*image-name*]
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Will create a new rbd image. You must also specify the size via --size. The
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--stripe-unit and --stripe-count arguments are optional, but must be used together.
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:command:`clone` [*parent-snapname*] [*image-name*]
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Will create a clone (copy-on-write child) of the parent snapshot.
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Object order will be identical to that of the parent image unless
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specified. Size will be the same as the parent snapshot.
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The parent snapshot must be protected (see `rbd snap protect`).
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This requires format 2.
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:command:`flatten` [*image-name*]
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If image is a clone, copy all shared blocks from the parent snapshot and
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make the child independent of the parent, severing the link between
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parent snap and child. The parent snapshot can be unprotected and
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deleted if it has no further dependent clones.
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This requires format 2.
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:command:`children` [*image-name*]
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List the clones of the image at the given snapshot. This checks
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every pool, and outputs the resulting poolname/imagename.
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This requires format 2.
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:command:`resize` [*image-name*]
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Resizes rbd image. The size parameter also needs to be specified.
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:command:`rm` [*image-name*]
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Deletes an rbd image (including all data blocks). If the image has
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snapshots, this fails and nothing is deleted.
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:command:`export` [*image-name*] [*dest-path*]
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Exports image to dest path (use - for stdout).
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:command:`import` [*path*] [*dest-image*]
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Creates a new image and imports its data from path (use - for
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stdin). The import operation will try to create sparse rbd images
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if possible. For import from stdin, the sparsification unit is
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the data block size of the destination image (1 << order).
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:command:`export-diff` [*image-name*] [*dest-path*] [--from-snap *snapname*]
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Exports an incremental diff for an image to dest path (use - for stdout). If
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an initial snapshot is specified, only changes since that snapshot are included; otherwise,
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any regions of the image that contain data are included. The end snapshot is specified
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using the standard --snap option or @snap syntax (see below). The image diff format includes
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metadata about image size changes, and the start and end snapshots. It efficiently represents
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discarded or 'zero' regions of the image.
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:command:`import-diff` [*src-path*] [*image-name*]
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Imports an incremental diff of an image and applies it to the current image. If the diff
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was generated relative to a start snapshot, we verify that snapshot already exists before
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continuing. If there was an end snapshot we verify it does not already exist before
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applying the changes, and create the snapshot when we are done.
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:command:`cp` [*src-image*] [*dest-image*]
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Copies the content of a src-image into the newly created dest-image.
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dest-image will have the same size, order, and format as src-image.
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:command:`mv` [*src-image*] [*dest-image*]
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Renames an image. Note: rename across pools is not supported.
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:command:`snap` ls [*image-name*]
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Dumps the list of snapshots inside a specific image.
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:command:`snap` create [*image-name*]
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Creates a new snapshot. Requires the snapshot name parameter specified.
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:command:`snap` rollback [*image-name*]
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Rollback image content to snapshot. This will iterate through the entire blocks
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array and update the data head content to the snapshotted version.
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:command:`snap` rm [*image-name*]
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Removes the specified snapshot.
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:command:`snap` purge [*image-name*]
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Removes all snapshots from an image.
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:command:`snap` protect [*image-name*]
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Protect a snapshot from deletion, so that clones can be made of it
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(see `rbd clone`). Snapshots must be protected before clones are made;
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protection implies that there exist dependent cloned children that
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refer to this snapshot. `rbd clone` will fail on a nonprotected
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snapshot.
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This requires format 2.
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:command:`snap` unprotect [*image-name*]
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Unprotect a snapshot from deletion (undo `snap protect`). If cloned
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children remain, `snap unprotect` fails. (Note that clones may exist
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in different pools than the parent snapshot.)
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This requires format 2.
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:command:`map` [*image-name*]
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Maps the specified image to a block device via the rbd kernel module.
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:command:`unmap` [*device-path*]
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Unmaps the block device that was mapped via the rbd kernel module.
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:command:`showmapped`
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Show the rbd images that are mapped via the rbd kernel module.
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:command:`lock` list [*image-name*]
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Show locks held on the image. The first column is the locker
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to use with the `lock remove` command.
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:command:`lock` add [*image-name*] [*lock-id*]
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Lock an image. The lock-id is an arbitrary name for the user's
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convenience. By default, this is an exclusive lock, meaning it
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will fail if the image is already locked. The --shared option
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changes this behavior. Note that locking does not affect
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any operation other than adding a lock. It does not
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protect an image from being deleted.
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:command:`lock` remove [*image-name*] [*lock-id*] [*locker*]
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Release a lock on an image. The lock id and locker are
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as output by lock ls.
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:command:`bench-write` [*image-name*] --io-size [*io-size-in-bytes*] --io-threads [*num-ios-in-flight*] --io-total [*total-bytes-to-write*]
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Generate a series of sequential writes to the image and measure the
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write throughput and latency. Defaults are: --io-size 4096, --io-threads 16,
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--io-total 1GB
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Image name
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==========
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In addition to using the --pool and the --snap options, the image name can include both
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the pool name and the snapshot name. The image name format is as follows::
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[pool/]image-name[@snap]
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Thus an image name that contains a slash character ('/') requires specifying the pool
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name explicitly.
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Striping
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========
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RBD images are striped over many objects, which are then stored by the
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Ceph distributed object store (RADOS). As a result, read and write
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requests for the image are distributed across many nodes in the
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cluster, generally preventing any single node from becoming a
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bottleneck when individual images get large or busy.
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The striping is controlled by three parameters:
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.. option:: order
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The size of objects we stripe over is a power of two, specifially 2^[*order*] bytes. The default
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is 22, or 4 MB.
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.. option:: stripe_unit
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Each [*stripe_unit*] contiguous bytes are stored adjacently in the same object, before we move on
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to the next object.
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.. option:: stripe_count
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After we write [*stripe_unit*] bytes to [*stripe_count*] objects, we loop back to the initial object
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and write another stripe, until the object reaches its maximum size (as specified by [*order*]. At that
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point, we move on to the next [*stripe_count*] objects.
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By default, [*stripe_unit*] is the same as the object size and [*stripe_count*] is 1. Specifying a different
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[*stripe_unit*] requires that the STRIPINGV2 feature be supported (added in Ceph v0.53) and format 2 images be
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used.
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Examples
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========
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To create a new rbd image that is 100 GB::
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rbd -p mypool create myimage --size 102400
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or alternatively::
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rbd create mypool/myimage --size 102400
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To use a non-default object size (8 MB)::
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rbd create mypool/myimage --size 102400 --order 23
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To delete an rbd image (be careful!)::
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rbd rm mypool/myimage
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To create a new snapshot::
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rbd snap create mypool/myimage@mysnap
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To create a copy-on-write clone of a protected snapshot::
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rbd clone mypool/myimage@mysnap otherpool/cloneimage
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To see which clones of a snapshot exist::
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rbd children mypool/myimage@mysnap
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To delete a snapshot::
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rbd snap rm mypool/myimage@mysnap
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To map an image via the kernel with cephx enabled::
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rbd map mypool/myimage --id admin --keyfile secretfile
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To unmap an image::
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rbd unmap /dev/rbd0
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To create an image and a clone from it::
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rbd import --format 2 image mypool/parent
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rbd snap create --snap snapname mypool/parent
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rbd snap protect mypool/parent@snap
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rbd clone mypool/parent@snap otherpool/child
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To create an image with a smaller stripe_unit (to better distribute small writes in some workloads)::
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rbd -p mypool create myimage --size 102400 --stripe-unit 65536 --stripe-count 16
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To change an image from one format to another, export it and then
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import it as the desired format::
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rbd export mypool/myimage@snap /tmp/img
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rbd import --format 2 /tmp/img mypool/myimage2
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To lock an image for exclusive use::
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rbd lock add mypool/myimage mylockid
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To release a lock::
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rbd lock remove mypool/myimage mylockid client.2485
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Availability
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============
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**rbd** is part of the Ceph distributed file system. Please refer to
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the Ceph documentation at http://ceph.com/docs for more information.
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See also
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========
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:doc:`ceph <ceph>`\(8),
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:doc:`rados <rados>`\(8)
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