UFS Snapshot lock time

[Jeremy Chadwick]

On Wed, Nov 12, 2008 at 08:22:29PM -0600, 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.

This topic comes up about once every 2 weeks.  There's a discussion
going about it on -stable right now:

http://lists.freebsd.org/pipermail/freebsd-stable/2008-November/046524.html

It's also been documented on my issues Wiki:

http://wiki.freebsd.org/JeremyChadwick/Commonly_reported_issues

At this time, there is no fix.  Workarounds:

1) Use rsnapshot (which is rsync-based) to accomplish the same; this
   works on a UFS/UFS2 filesystem.  However, note that file atimes on
   your source will get destroyed (which will affect the "new mail"
   capability of classic UNIX mboxes; there is no solution for that)
1) Switch to ZFS, which has a reliable snapshotting.

> In theory, this should be a rather fast box, but it is a rather large  
> filesystem.

The speed of the box has nothing to do with the problem; your hardware
is not to blame.

-- 
| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |