[linux-lvm] Re: Proper method of snapshotting XFS with external log using LVM2

[Milan Broz]

Mario Becroft wrote:
> 2. I tried without xfs_freeze anyway just to see what would happen, and
> actually in kernel 2.6.22.1 if you simply create a snapshot of the main
> filesystem volume and destroy it several times in a row (not even
> touching the log volume yet) lvcreate hangs.

Well, probably two problems combined here. 

In 2.6.22 is change in block layer which serializes generic_make_request()
calls and it causes some problems with synchronous metadata snapshot updates.
See patch which moves metadata updates to separate thread
http://www2.kernel.org/pub/linux/kernel/people/agk/patches/2.6/2.6.22/dm-snapshot-fix-invalidation-deadlock.patch

Maybe lvcreate hang is just another demonstration of this problem.

Please could you test it with 2.6.21 kernel, or with kernel with this patch applied ?

Is the bug with separate filesystem log reported in bugzilla ?

If you find problem with even patch above, please report it with
exact description how you reach this.

Milan
--
mbroz at redhat.com