chen@admin-node:~$ rbd --help
usage: rbd [-n <auth user>] [OPTIONS] <cmd> ...
where \'pool\' is a rados pool name (default is \'rbd\') and \'cmd\' is one of:
  (ls | list) [-l | --long ] [pool-name] list rbd images
                                              (-l includes snapshots/clones)
  info <image-name>                           show information about image size,
                                              striping, etc.
  create [--order <bits>] [--image-features <features>] [--image-shared]
         --size <MB> <name>                   create an empty image
  clone [--order <bits>] [--image-features <features>] [--image-shared]
        <parentsnap> <clonename>              clone a snapshot into a COW
                                              child image
  children <snap-name>                        display children of snapshot
  flatten <image-name>                        fill clone with parent data
                                              (make it independent)
  resize --size <MB> <image-name>             resize (expand or contract) image
  rm <image-name>                             delete an image
  export <image-name> <path>                  export image to file
                                              "-" for stdout
  import [--image-features <features>] [--image-shared]
         <path> <image-name>                  import image from file (dest
                                              defaults as the filename part
                                              of file). "-" for stdin
  diff <image-name> [--from-snap <snap-name>] print extents that differ since
                                              a previous snap, or image creation
  export-diff <image-name> [--from-snap <snap-name>] <path>
                                              export an incremental diff to
                                              path, or "-" for stdout
  merge-diff <diff1> <diff2> <path>           merge <diff1> and <diff2> into
                                              <path>, <diff1> could be "-"
                                              for stdin, and <path> could be "-"
                                              for stdout
  import-diff <path> <image-name>             import an incremental diff from
                                              path or "-" for stdin
  (cp | copy) <src> <dest>                    copy src image to dest
  (mv | rename) <src> <dest>                  rename src image to dest
  snap ls <image-name>                        dump list of image snapshots
  snap create <snap-name>                     create a snapshot
  snap rollback <snap-name>                   rollback image to snapshot
  snap rm <snap-name>                         deletes a snapshot
  snap purge <image-name>                     deletes all snapshots
  snap protect <snap-name>                    prevent a snapshot from being deleted
  snap unprotect <snap-name>                  allow a snapshot to be deleted
  watch <image-name>                          watch events on image
  status <image-name>                         show the status of this image
  map <image-name>                            map image to a block device
                                              using the kernel
  unmap <device>                              unmap a rbd device that was
                                              mapped by the kernel
  showmapped                                  show the rbd images mapped
                                              by the kernel
  lock list <image-name>                      show locks held on an image
  lock add <image-name> <id> [--shared <tag>] take a lock called id on an image
  lock remove <image-name> <id> <locker>      release a lock on an image
  bench-write <image-name>                    simple write benchmark
                 --io-size <bytes>              write size
                 --io-threads <num>             ios in flight
                 --io-total <bytes>             total bytes to write
                 --io-pattern <seq|rand>        write pattern

<image-name>, <snap-name> are [pool/]name[@snap], or you may specify
individual pieces of names with -p/--pool, --image, and/or --snap.

Other input options:
  -p, --pool <pool>                  source pool name
  --image <image-name>               image name
  --dest <image-name>                destination [pool and] image name
  --snap <snap-name>                 snapshot name
  --dest-pool <name>                 destination pool name
  --path <path-name>                 path name for import/export
  --size <size in MB>                size of image for create and resize
  --order <bits>                     the object size in bits; object size will be
                                     (1 << order) bytes. Default is 22 (4 MB).
  --image-format <format-number>     format to use when creating an image
                                     format 1 is the original format (default)
                                     format 2 supports cloning
  --image-features <features>        optional format 2 features to enable
                                     +1 layering support, +2 striping v2,
                                     +4 exclusive lock, +8 object map
  --image-shared                     image will be used concurrently (disables
                                     RBD exclusive lock and dependent features)
  --stripe-unit <size-in-bytes>      size (in bytes) of a block of data
  --stripe-count <num>               number of consecutive objects in a stripe
  --id <username>                    rados user (without \'client.\'prefix) to
                                     authenticate as
  --keyfile <path>                   file containing secret key for use with cephx
  --shared <tag>                     take a shared (rather than exclusive) lock
  --format <output-format>           output format (default: plain, json, xml)
  --pretty-format                    make json or xml output more readable
  --no-progress                      do not show progress for long-running commands
  -o, --options <map-options>        options to use when mapping an image
  --read-only                        set device readonly when mapping image
  --allow-shrink                     allow shrinking of an image when resizing