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Configure option to disable BACKUP LOG TO DISK = 'NUL' by Stan Segers


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Type: Suggestion
ID: 795081
Opened: 7/26/2013 1:56:24 AM
Access Restriction: Public
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Description

In some cases I had problems with virtual machines and VSS based backup software. These problems are twofold;
- VSS based backups software executing a BACKUP LOG TO DISK = 'NUL' after taking a snapshot and thus invalidating the log chain.
- VSS based backup software taking full backups under the hood (thus resetting the base for differential backups)

For the first issue, I found the culprit; Veeam (http://www.veeam.com/vmware-backup/help-center/hyperv/index.html?transaction_truncation.html; http://www.veeam.com/vmware-backup/help-center/vsphere/index.html?transaction_truncation.html). To avoid this problem, I would like to have an option (under sp_configure) to disallow log backups to disk = 'NUL'

For the second issue, a seperate connect item exits: "Option to force VSS backup to copy_only" https://connect.microsoft.com/SQLServer/feedback/details/790560
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Posted by Harut on 4/4/2014 at 4:16 PM
I think the request is not to completely disallow BACKUP LOG TO DISK = 'NUL' which I agree can be invaluable, but to have the knob to disable it as a conscious choice. You can always keep the default for a "Disallow" option to "off"
Posted by Microsoft on 10/10/2013 at 2:51 PM
VSS backups do not perform any form of LOG backup. The only options for VSS-based SQL backups are FULL and Database. If something is taking a BACKUP LOG TO NULL operation, it is the application, and not VSS.
While it would be handy to prevent backups to NULL, there area few areas where it is an invaluable tool (such as when the DB is completely out of disk space for the log, which can't truncate for lack of a backup.) This does break the log chain but that's better than having production down.
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