On site full required?

[timvan007]

We are adding some storage to our SAN and the question was asked why do we need additional disk storage for backups in addition to the file storage. Valid question, one to which I normally answer with best practices to back up to disk and duplicate to tape. Though, technically there is nothing stopping me from going directly to tape.

That being said, we send all tapes off site once a day. If I would send a full backup off site, would I still be able to run a differential without it on site? I am using BE 2014 SP1. The backups would be agent based file level backups of Windows Server 2012 Standard. Right now I back up using modified time for these types, but not sure if archive bit or catalog based would help in this situation.

I may be able to sway to the side of sending Full backups off site and keeping diffs on site. Does anyone know if I can restore from a Diff on disk if the full backup is not available. Again, for VMWare GRT AVVI backups and restore, I normally need both full and diff, but for differential agent based file backups, I think I might be able to restore just from the diff.

[lmosla]

For file backups it would be much safer to keep a full backup on site since the differential will only restore a file that has been changed since the full backup.  If you need to restore a file that gets deleted and it hasn't been changed since the most recent full backup the file will need full backup to be restored.

[pkh · Accepted solution]

Although you can do differential/incremental backups when the full backup is not present, it is a different story when you do a restore. Unlike previous versions of BE, from BE 2012 onwards, BE automatically restore the entire backup chain when you restore a differential/incremental backup.  As such you should always have your full backup ready when you do a restore.  See this blog

https://www-secure.symantec.com/connect/fr/blogs/simplified-restore-workflow-be-2012

Although there is nothing to stop you from putting your full backup on tape and your differential backup on disk.  I don't know how your differential backup will be handled by DLM which manages disk storage and expects the entire backup chain to be present on disk.

It would be a better strategy to do B2D2T for both your full and incremental backups, but to save on disk space, have either no retention or very short retention periods for your disk backup sets.  By default, DLM will keep the last recovery point, i.e. the last backup chain.  See this blog and my article below

https://www-secure.symantec.com/connect/fr/blogs/data-lifecycle-management-be-2012

https://www-secure.symantec.com/connect/articles/when-backup-sets-are-deleted-under-dlm

[timvan007]

Thanks PKH, I did not think about DLM when I got the idea to at least keep diffs on disk. And you're right, that would most likely wreak havoc on the storage management. 

I acknowledge it is best practice to do B2D2T, and that is my goal. I am just held to present all *possible* options, and B2T is technically possible even if it is not optimal. I will lobby for the additional disk storage, but thanks for the info. It's rather easy to say "every time you need a file restored, I'll need to request tapes and wait 24 hours for the full" but there's always the chance that'll be acceptable for low-tier files.