September 25, 2012 at 6:26 am
The company which i work for have just introduced Veeam backup and replication as the method of backing up the VMware environment.
We have an SQL Server instance running on one of the VM's which is now being backed up by Veeam and i have noticed that the entry in the MSDB table which corresopnds to the Veeam backup job is in fact a Snaphot Backup (the is_snapshot column has a value of 1).
There seems to be a real lack of information out there with regards to the snapshot backups within SQL Server and i'm keen to understand how it works. I understand that VSS is used but i can't seem to find out much beyond that.
I'm keen to know if backup files are actually produced, how restores work with this kind of backup, what affect it has on an SQL Server backup chain, etc.
If anyone can point me towards a good source of information on the subject it would be greatly appreciated, or if anyone on here has expereince and can shed some light on it for me iw ould be similarly greatful.
Thanks.
December 18, 2012 at 6:26 am
January 2, 2013 at 11:47 am
I feel that one of the terms that should be banned is "snapshot backup." The term "backup" implies that as long as you have the backup file, you'll be able to restore the DB to the point it was at when the backup was made. With snapshots, this may NOT be the case.
This is because the snapshot contains only the unaltered data pages than have been altered in the database file since the snapshot was created. The advantage of this is that snapshots are fast to create and may be faster to restore than full backups, but if you lose the database file (such as from a hard drive failure) then the snapshot is useless.
Also, if you are doing massive changes to a database you intend to undo with a snaopshot restore, and the I/O cannot keep up, you may end up with snapshot than cannot be restored. This happened to me last year when I made a snapshot to a 500GB DB before deleting most of the data, running a SRINKFILE, an upgrade form the software vendor, a backup to create a new version of the database, then tried to restore it using the snapshot. I thought I was saving a couple hours by not running a full backup first, but it turned out that the snapshot had been corrupted from an I/O error and could not be used. If I made a full backup prior to making the major changes I would have been fine.
Snapshots will not affect the backup chain. However, you must drop any existing snapshots before restoring from a fulll backup.
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