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questions on backup of XEN's VM

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Hi, we installed Linux Agents on two Xen's VMs locally and both VMs are running CentOS v6.5 and v.7.3. Questions:

  1. How does Acronis agent do the backup? (e.g. taking some kind of snapshot or backing up files by files, etc).
  2. How does it handle locked files?
  3. We have either mysql or postgresql  database running. The file timestamp and file size may not change even changes made to the databases. Do I need to turn off "Use fast incremental/differential backup" option? (I'm afraid that Acronis will not backup the file when file size and timestamp remain the same)? If we turn off "fast incremental", will it extend the backup time too much (we have database file size around 30 GB or larger)

Thanks,

Aldous

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Hello Comwave IT,

Acronis Backup is able to perform snapshot-based backup of Linux environment. It can do its own snapshot or use LVM-snapshots. The difference between these snapshots is the way how data is saved after snapshot is created. 
 
Once a volume snapshot is taken, and the data starts changing, the old data has to be kept somewhere until it is saved to the backup. 
Acronis keeps the old data mostly in the RAM. (During a file-level backup, the software may create a temporary file in /tmp if the old data size significantly grows.) 
LVM needs a temporary logical volume (a snapshot logical volume) for keeping the old data (see Taking a Backup Using Snapshots). Writing this data onto the volume causes a large number of disk I/O operations. This is why the backup is usually slower when a snapshot is taken by LVM.

If the file size and the timestamps don't change, then Fast incremental/differential backup feature won't bring the advantage either. I'd suggested disabling this option and see if the times differ significantly. 

So, how do I know and control my backup to perform snapshot (non-LVM) or file based? I used mostly default settings when creating backup plan. Thanks

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Posts: 250
Comments: 7092

Snapshot is always created before backup, to double-check it's been successful you may want looking through the operation log of the backup job. In addition to the default snapshot option, you can also use

SAN hardware snapshots
Multi-volume snapshot
LVM snapshotting
File-level backup snapshot

these options are useful in particular scenarios.