LVM snapshot

Bill Rugolsky Jr. brugolsky at telemetry-investments.com
Fri Aug 13 12:17:04 UTC 2004


On Thu, Aug 12, 2004 at 11:09:25PM +1000, Russell Coker wrote:
> > Did I do something wrong or is this an indication of a kernel bug in LVM?

Which kernel, the FC2 errata kernel?  Probably just a problem with the
userspace side; grab the RPMS from Rawhide.

I've been playing with snapshots since kernel-2.6.7-1.471 (i.e.,
2.6.7-bk18) on both FC2 and FC1, using packages from Rawhide.  I have
another machine running 2.6.7-1.492 (2.6.7-rc1) that also seems to work,
though it hasn't been tested much.  (Both kernels patched and rebuilt
without 4G/4G.)

Snapshot performance was not particularly good (on soft-RAID1), but I ran
bonnie++ on an 8GB filesystem with a snapshot in place, and it survived,
even while running cpio -o > /dev/null on the snapshot.  I need to find
time to roll my patches forward, retest, and look at the tunables.

> I just tried rebooted that machine.  The LVM setup seems mangled and it 
> doesn't boot successfully.
 
I encountered a "gotcha" when using snapshots (or DM mirror): if using an
initrd, one needs to place those modules (dm-snapshot, dm-mirror)
in the initrd, otherwise LVM2 won't activate the LVs when you reboot.

Alexandre, where should this config info live?  Historically, we had the
loop stuff in /etc/fstab; thankfully, dependence on loop is going away.

Regards,

	Bill Rugolsky





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