VxVM Volume Snapshot Part One - 系列之卷快照的创建

【VxVM Volume Snapshot 系列文章】
  1.《VxVM Volume Snapshot Part One - 系列之卷快照的创建》
  2.《VxVM Volume Snapshot Part Two - 卷快照的删除》
  3.《VxVM Volume Snapshot Issue – 卷快照删除失败示例一》

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【卷快照的创建】
  本文简单描述VxVM space-optimized instant snapshot的创建流程，内容基于Veritas Offical DOC，若有不当之处，敬请指正！

/*
* Steps to take a VxVM volume space-optimized instant snapshot
*/ 
0. Make sure the formar snapshot of current volume is deleted, if not, you cannot create a new snapshto with the same name. The delete process will be describled in bolg: ......
1. vxsnap prepare. It creates a DCO and DCO volume that allow instant snapshots and Persistent FastResync to be used with the volume, and associates this with the volume. It also enables Persistent FastResync on the volume. 
   # vxsnap [-g diskgroup] prepare [volume]
2. Enable the fastresync if it is not enabled in step 1. Following command returns on if FastResync is enabled; otherwise, it returns off.
   # vxprint [-g diskgroup] -F%fastresync [volume]
   // if the return is off, we should try to turn on if using following command and then do re-check
   # vxvol [-g diskgroud] set fastresync=on [volume]
3. Ensure the volume is prepared. If unprepared, you should do unprepare and prepare commands again
   # vxprint [-g diskgroup] -F%instant [volume]
4. Create the cache volume and attache it to a cache object and then start the cache object
   # vxassist [-g diskgroup] make [cache_volume] [size][G|M]
   # vxmake [-g diskgroup] cache [cache_object] cachevolname=[cache_volume]
   # vxcache [-g diskgroup] start [cache_object]
5. Freeing or pausing replication
       Before taking the snapshot on the Secondary, make sure the data volumes are consistent at the application level by either freezing or pausing     
   replication. To make the data volumes consistent at the application level, use the IBC messaging utility vxibc. For information on using the vxibc 
   utility, refer to Using VVR for off-host processing. For a failed Primary, you can pause the Primary RLINK, and then take a snapshot of the RVG. If 
   you do not use vxibc, you pause the RLINK before taking the snapshot.
       VVR provides you with sample scripts that can be used to freeze the replication before creating instant snapshots. When you install VVR, these 
   scripts are installed in the following directory: /etc/vx/vvr/ibc_scripts/sample_so_snapshot
       Refer to the README file in this directory for instructions on how to use the sample scripts to create the instant snapshots.
6. vxsnap make step creates an instant snapshot that is immediately available for making a backup. After the snapshot taken sucessfully, both the original volume and the new taken snapshot can support reading operation
   # vxsnap [-g diskgroup] make source=[volume]/newvol=[snapshot_volume]/cache=[cache_object]
7. Unfreezing or resuming replication
   After taking a snapshot, unfreeze replication if you are using IBC messaging; otherwise, if you have paused replication, resume it. The snapshots are now ready for use.