Verifying Backups

[enjay]

During a conversation with support at the company that makes our backup software, I was told that verifying backups is only necessary when using tapes, and isn't needed on D2D backups. Obviously he knows more about this than I do, but it seems a little risky not to be checking in that way - my spot-check restores will only pick up so much, after all. What are other people's thoughts?

[Duke]

I was told you don't need to as well as its primary purpose is for picking up media-write errors, which really shouldn't occur with disks but are possible with tape. I still verify anyway as unless you're restoring a lot of data regularly there's no other way to tell if your backups are really working. If your backups are taking too long and you need to save time then maybe only verify the weekly backups and just trust the daily backups?

 

Cheers,

Chris

[powdarrmonkey]

I was told you don't need to as well as its primary purpose is for picking up media-write errors, which really shouldn't occur with disks but are possible with tape.

 

Er... am I the only one that has write errors on disks then? If a disk is on the way out you'll see exactly the same behaviour as with a tape. The point of a verify is to read back the data you've backed up and see if it corresponds with what is on the source, and that's important whatever media you write to.

[Duke]

Good point, I guess most people just look at it in the way that with a disk you should already have some kind of RAID redundancy and if a device is failing then you'll either be notified by Windows (if it's a server) or the SAN software, whereas a tape could be failing and you wouldn't know until you tried to restore data from it, and that single tape may be the only place the data is stored.

 

I think verifying data is still a good idea (like I said, we still do it on D2D) but if you assume your disk system is working as designed and will alert you in the case of disk failures then in theory you won't need to verify your disk backups as you'll know if you have disk failure (and will be covered by RAID if you do).

 

Unless you really need to turn off verification for any reason, might as well leave it on.

Chris

[powdarrmonkey]

No. Memory corruption in the backup process that then gets written correctly, even to a RAID array, won't be right and won't be reported. The only reliable way to detect this is a verify after the event.

[Martin]

Back in the days of proper computers, backups consisted of an "image" copy (not physical, in case there were bad blocks) from one removable disk to another (e.g. the 205Mb RA60), and then swap the backup to become live - that way you knew straight away if there was a problem!

 

http://hampage.hu/vax/egyeb/ra60.jpg

 

...you can never be too careful when doing backups!

 

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