Differential backups rendered useless by backup device

SQLServerCentral is supported by Red Gate Software Ltd.

Popular Topics

Home

Members

Calendar

Who's On

Home » SQL Server 2008 » SQL Server 2008 Administration » Differential backups rendered useless by...

15 posts, Page 2 of 2

««1 2

Differential backups rendered useless by backup device

Rate Topic

Display Mode

Topic Options

Author

Message

sqlskj4000

Posted Wednesday, February 20, 2013 1:59 PM

Forum Newbie

Group: General Forum Members
Last Login: Saturday, June 15, 2013 10:37 AM
Points: 5, Visits: 54

You could create an after-insert trigger on 'backupset' table in msdb database. Check for the condition is_snapshot=1 and run the full backup job.
This is a good idea. But luckily for me, something changed in the backup plan of the n/w admins and I didn't see those annoying snapshot entries anymore.

Post #1422293

GilaMonster

Posted Wednesday, February 20, 2013 2:10 PM

SSC-Dedicated

Group: General Forum Members
Last Login: Today @ 4:08 PM
Points: 38,099, Visits: 30,392

rferreira.dba (2/20/2013)

Let me put this another way: Is there any valid reason for Microsoft not to fix this?

Because there's nothing broken here?
The kb article you referenced refers to a problem where an incorrect insert is made into the backup history tables reflecting a backup that did not happen, not the case where you really are taking valid backup of the database. The backup history tables do not drive valid restores, they're just a record of what backups happen. The issue you have is not related to that kb article.

In your case, you are taking two types of full backups and the differential that runs is correctly based on the latest full (whatever it may be). This isn't a bug, this is documented, normal behaviour
You can get into exactly the same mess with two scheduled of native backups, where one is taken off site and not available. A differential backup is always based on the latest non-copy only full backup

Is this possible? Is there an after_successful_snapshot trigger somewhere, or something similar that I can use?

As far as SQL is concerned, that's just a database backup run by a 3rd party product. No less valid or correct than a normal database backup. Can you hook into whatever is running the snapshot backups and have that run some SQL afterwards?

Options:
- Set the backup app to snapshot the machine but exclude the databases. Some tools can, some can't. If you have a good SQL backup strategy, as it sounds like you have, then there isn't a need to snapshot the databases as well.
- Set the backup app to do a 'copy only' snapshot. Probably won't be an option, haven't seen that as a setting in many tools.
- Change the backup strategy to be a mix of full and log backups. If you're not doing differentials then the additional full backups won't have any effect on restoring. Not the best option, probably the last option if nothing else is possible

p.s. This is why I always say that all SQL backups should be done the same way and that there should only be one method for the SQL backups. Native or 3rd party, not a mix of both.

Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Post #1422298

sqlskj4000

Posted Wednesday, February 20, 2013 2:54 PM

Forum Newbie

Group: General Forum Members
Last Login: Saturday, June 15, 2013 10:37 AM
Points: 5, Visits: 54

I agree it's not exactly a bug. But the fact remains that differentials are running based on a non-existent full backup (a backup that's part of a volume snapshot). It could've been avoided if the VSS writer recorded it as 'copy only'.
And I agree that there should be only one method of backup. But in my case we require both. Volume snapshot is the preferred restoration method, in case of a crash. SQL maintenance plans are our fallback option.
If we don't have access to the backup device to check it's options, it's either your third option or the option proposed by rferreira (full backup immediately after the snapshot).

Post #1422324

GilaMonster

Posted Wednesday, February 20, 2013 3:07 PM

SSC-Dedicated

Group: General Forum Members
Last Login: Today @ 4:08 PM
Points: 38,099, Visits: 30,392

sqlskj4000 (2/20/2013)

Agreed, the problem there is that many of the tools that use the VSS writer to back up a SQL database don't have an option for the user to set copy only, and it is not (and cannot be) the default.

Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Post #1422329

Nadrek

Posted Thursday, February 21, 2013 10:16 AM

Say Hey Kid

Group: General Forum Members
Last Login: Monday, June 10, 2013 1:08 PM
Points: 679, Visits: 2,038

Gail beat me to the "change to Full recovery model and do Log backups instead" option.

As far as your proposed "full after each snapshot" option, you can try looking at extended events, as well as seeing if Windows Task Scheduler can trigger off of the snapshot (then you use sqlcmd to run msdb.dbo.sp_start_job), but the brute-force way is to set up a job that polls every N minutes in about the right timerange, and compare the msdb list of snapshot backups to a stateful list of prior snapshot backups. When it sees a new one, kick off a full backup and record the new snapshot.

Personally, I'd have to say that Gail's options are the best - your Full backup after the snapshot may fail for a variety of reasons, leaving your every 4 hour Differential backups silently worthless.

Post #1422697

« Prev Topic | Next Topic »

15 posts, Page 2 of 2

««1 2

Permissions