UFS Snapshot lock time

[Javier Martín Rueda]

Kevin Day wrote:
>
> Is there any documentation out there that explains how to optimize UFS 
> snapshotting?
>
> Specifically, we've got a rather big filesystem that I'd like to do 
> hourly snapshots of. I don't mind how long the snapshot itself takes, 
> but the amount of time the filesystem is locked is a problem. We're 
> "dead" for about 12 minutes per snapshotting.
>
Just a word of caution: I used to do this in some different machines 
(taking periodic snapshots and leaving a few around), and after a few 
days or weeks the system would lock up. Any process accessing the 
filesystem would block in "ufs" or something like that. After rebooting, 
fsck would report fatal errors and I had to do fsck -y in order to fix 
them with plenty of scary messages about truncated inodes, unexpected 
inconsistencies, and so on. This happened in several 6.x releases, on 
different machines, and both under i386 or amd64. Eventually, I gave up.

I strongly suggest you try taking hourly snapshots in a non-production 
system first for a few weeks, and see if you experience this kind of 
problems. Sorry to be a party-pooper.

It looks as if keeping more than one snapshot eventually is problematic. 
Taking single snapshots for dump has never been a problem, though.