UFS Snapshot lock time

[Kevin Day]

On Nov 13, 2008, at 10:11 AM, Javier Martín Rueda wrote:
> 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.
>

We definitely saw this problem in 6.x. Any reboot after a snapshot  
would be a mess of fsck fun for a few hours, usually resulting in us  
losing stuff. But, 7.0 has cured that for me.

So far hourly/daily snapshots on any of the 7.0 boxes we've tried it  
on has worked, it's just so slow it's unusable.  I'd like to think  
it's just being slow because it's being very careful. :)

-- Kevin