目的：阅读官方文档，熟悉rbd命令。
rbd命令行参数：
image相关
列出pools
root@maqi-openstack:~$ ceph osd lspools0 rbd,1 cephfs_data,2 cephfs_metadata,3 .rgw.root,4 .rgw.control,5 .rgw,6 .rgw.gc,7 .users.uid,
这里显示了0 ~ 7共8个pool。
The default pools include:
- data
- metadata
- rbd
创建image
root@maqi-openstack:~$ rbd create foo --size 1024
列出image
root@maqi-openstack:~$ rbd lsfooroot@maqi-openstack:~$ rbd ls rbd #rbd是默认poolfoo
查看image详细信息
root@maqi-openstack:~$ rbd --image foo inforbd image 'foo': size 1024 MB in 256 objects order 22 (4096 kB objects) block_name_prefix: rb.0.102b.74b0dc51 format: 1root@maqi-openstack:~$ rbd --image foo -p rbd inforbd image 'foo': size 1024 MB in 256 objects order 22 (4096 kB objects) block_name_prefix: rb.0.102b.74b0dc51 format: 1
Resize image
root@maqi-openstack:~$ rbd resize --image foo --size 2048Resizing image: 100% complete...done.root@maqi-openstack:~$ rbd --image foo inforbd image 'foo': size 2048 MB in 512 objects order 22 (4096 kB objects) block_name_prefix: rb.0.102b.74b0dc51 format: 1
删除image
root@maqi-openstack:~$ rbd rm foo -p rbdRemoving image: 100% complete...done.root@maqi-openstack:~$ rbd lsroot@maqi-openstack:~$ rbd --image foo info2015-10-12 15:56:48.457090 7f81b9afc840 -1 librbd::ImageCtx: error finding header: (2) No such file or directoryrbd: error opening image foo: (2) No such file or directory
snapshot相关
snapshot可以这样表示：
{pool-name}/{image-name}@{snap-name} 创建snapshot
root@maqi-openstack:~$ rbd --pool rbd snap create --snap snapname fooroot@maqi-openstack:~$ rbd --pool rbd snap ls fooSNAPID NAME SIZE 2 snapname 1024 MB
或者
root@maqi-openstack:~$ rbd snap create rbd/foo@snapshotroot@maqi-openstack:~$ rbd snap ls rbd/fooSNAPID NAME SIZE 2 snapname 1024 MB 3 snapshot 1024 MB
Rollback snapshot
Rolling back an image to a snapshot means overwriting the current version of the image with data from a snapshot. The time it takes to execute a rollback increases with the size of the image. It is faster to clone from a snapshot than to rollback an image to a snapshot, and it is the preferred method of returning to a pre-existing state.
root@maqi-openstack:~$ rbd --pool rbd snap rollback --snap snapname fooRolling back to snapshot: 100% complete...done.
或者
root@maqi-openstack:~$ rbd snap rollback rbd/foo@snapshotRolling back to snapshot: 100% complete...done.
删除snapshot
root@maqi-openstack:~$ rbd --pool rbd snap rm --snap snapname fooroot@maqi-openstack:~$ rbd snap rm rbd/foo@snapshot
snapshot layering
Ceph supports the ability to create many copy-on-write (COW) clones of a block device shapshot. Snapshot layering enables Ceph block device clients to create images very quickly. For example, you might create a block device image with a Linux VM written to it; then, snapshot the image, protect the snapshot, and create as many copy-on-write clones as you like. A snapshot is read-only, so cloning a snapshot simplifies semantics–making it possible to create clones rapidly.
Each cloned image (child) stores a reference to its parent image, which enables the cloned image to open the parent snapshot and read it.
A COW clone of a snapshot behaves exactly like any other Ceph block device image. You can read to, write from, clone, and resize cloned images. There are no special restrictions with cloned images. However, the copy-on-write clone of a snapshot refers to the snapshot, so you MUST protect the snapshot before you clone it. The following diagram depicts the process.
- snapshot都是read-only的
- 对snapshot做clone，利用了COW方式，生成新的image
使用snapshot layering时（也就是多次snapshot）：
- 对image创建snapshot
- protect这个snapshot，使其成为parent snapshot
- clone这个parent snapshot。clone出来的image就像一个普通的image。
Protect a snapshot
root@maqi-openstack:~$ rbd snap create --pool rbd --snap parent_snap fooroot@maqi-openstack:~$ rbd snap protect --pool rbd --snap parent_snap foorbd: protecting snap failed: (38) Function not implemented2015-10-13 06:31:42.966603 7fc2ecf95840 -1 librbd: snap_protect: image must support layering
只有format 2的image支持layering：
op@ubuntu-op:~$ sudo rbd create bar --image-format 2 --size 1024op@ubuntu-op:~$ sudo rbd snap create rbd/bar@parent_snapop@ubuntu-op:~$ sudo rbd snap protect rbd/bar@parent_snapop@ubuntu-op:~$ sudo rbd ls # 只列出imagebarop@ubuntu-op:~$ sudo rbd ls -l # 列出image和snapshotNAME SIZE PARENT FMT PROT LOCKbar 1024M 2bar@parent_snap 1024M 2 yes
protect之后不能删除：
op@ubuntu-op:~$ sudo rbd snap rm rbd/bar@parent_snaprbd: snapshot 'parent_snap' is protected from removal.2015-10-13 15:18:57.462634 7fe483d067c0 -1 librbd: removing snapshot from header failed: (16) Device or resource busy
Clone a snapshot
op@ubuntu-op:~$ sudo rbd clone rbd/bar@parent_snap rbd/bar_child_1op@ubuntu-op:~$ sudo rbd ls barbar_child_1op@ubuntu-op:~$ sudo rbd ls -lNAME SIZE PARENT FMT PROT LOCKbar 1024M 2bar@parent_snap 1024M 2 yesbar_child_1 1024M rbd/bar@parent_snap 2
注意：
- clone出来的东东是image，而不是snapshot
- clone命令只能针对snap，不能直接clone image：
op@ubuntu-op:~$ sudo rbd clone bar rbd/bar_child_2rbd: snap name was not specified
Unprotect a snapshot
op@ubuntu-op:~$ sudo rbd snap unprotect rbd/bar@parent_snap2015-10-13 15:25:01.553498 7faa3eac97c0 -1 librbd: snap_unprotect: can't unprotect; at least 1 child(ren) in pool rbdrbd: unprotecting snap failed: (16) Device or resource busyop@ubuntu-op:~$ sudo rbd rm rbd/bar_child_1Removing image: 100% complete...done.op@ubuntu-op:~$ sudo rbd snap unprotect rbd/bar@parent_snap
查看某个snapshot有没有被clone过（使用children命令）
op@ubuntu-op:~$ sudo rbd children rbd/bar@parent_snaprbd/bar_child_1
Flatten a child image
Cloned images retain a reference to the parent snapshot. When you remove the reference from the child clone to the parent snapshot, you effectively “flatten” the image by copying the information from the snapshot to the clone. The time it takes to flatten a clone increases with the size of the snapshot. To delete a snapshot, you must flatten the child images first.
op@ubuntu-op:~$ sudo rbd flatten bar_child_1Image flatten: 100% complete...done.op@ubuntu-op:~$ sudo rbd ls -lNAME SIZE PARENT FMT PROT LOCKbar 1024M 2bar@parent_snap 1024M 2 yesbar_child_1 1024M 2
RBD layering
简单来说，就是使用rbd clone命令，从image的某个snapshot克隆出一个新的image。
Incremental snapshot
针对image，rbd有3个diff命令，可以比较image的变化：
diff, export-diff, import-diff 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.
image bar有两个snapshot：
op@ubuntu-op:~$ sudo rbd snap create rbd/bar --snap bar_snap_2op@ubuntu-op:~$ sudo rbd snap list barSNAPID NAME SIZE 3 parent_snap 1024 MB 5 bar_snap_2 1024 MB
查看bar从创建以来的改动，输出到标准输出（因为没有改动，所以为空）：
op@ubuntu-op:~$ sudo rbd export-diff bar -rbd diff v1Exporting image: 100% complete...done.
查看bar从snapshot parent_snap以后的改动，输入到文件中：
op@ubuntu-op:~$ sudo rbd export-diff bar diff_1 --snap parent_snapExporting image: 100% complete...done.op@ubuntu-op:~$ cat diff_1rbd diff v1t parent_snaps@eop@ubuntu-op:~$ file diff_1diff_1: data
用export-diff取得diff文件后，可以用import-diff把这个diff文件import到某个image中
op@ubuntu-op:~$ sudo rbd import-diff diff_1 barend snapshot 'parent_snap' already exists, abortingImporting image diff: 0% complete...failed.op@ubuntu-op:~$ sudo rbd import-diff diff_1 bar_child_1Importing image diff: 100% complete...done.
rbd import-diff /path/to/diff backup_image
This will write the contents of the differential to the backup_image and create a snapshot with the same name as the original ending snapshot. It will fail and do nothing if a snapshot with this name already exists. Since overwriting the same data is idempotent, it’s safe to have an import-diff interrupted in the middle.