[linux-lvm] Re: Summary - Snapshot Effort

[Eric Sandeen]

On Thu, 2002-08-22 at 16:43, Greg Freemyer wrote:
> All,
> 
> I have not been successful at getting reliable Read-Only snapshots of XFS via LVM.  Since XFS is being used in Enterprise quality applications, I suggest this is a major shortcoming that should be prioritized.
> 
> BTW: Are there any snapshot related tests in the XFS regression tests?

No, there aren't.  Frankly, snapshot has not gotten a lot of attention
lately.

> When a failure occurs the lvcreate --snapshot command will freeze up.    

If that's the failure, looking at a kdb backtrace of the "stuck" process
would be helpful, and might give us an idea of where to look.

Testing a CVS kernel for the same behavior would also be a good
datapoint.
 
> A manually entered xfs_freeze -u will release the lvcreate.  (The VFS-lock patch effectively is calling xfs_freeze -f internally prior to starting the snapshot process.)

> FYI: Adrian Head believes that the VFS-lock patch is more reliable than not having it and wrapping the lvcreate --snapshot call with explicit xfs_freeze calls.  I have not tried that.

If things are working as intended, that should not be the case - the end
result should be that xfs runs the same code, whether you did it via a
manual userspace command, or the automatic vfs-lock patch.

Sending some debug output from kdb would help - but also, take a look at
that list of work Steve posted today, and realize that there are lots of
things going on at the moment.  :)

Thanks,
-Eric


-- 
Eric Sandeen      XFS for Linux     http://oss.sgi.com/projects/xfs
sandeen at sgi.com   SGI, Inc.         651-683-3102