[linux-lvm] Another XFS + LVM2 snapshots problems

[linux-lvm] Another XFS + LVM2 snapshots problems

[Gabriel Barazer]

Hello,

Although I often read in the mailing archive that XFS and snapshots aren't 
good friends, this filesystem is the best for my use (a file server with 
~2.5M files and files > 2GB). Now is the time to do snapshots. Here many 
problems occurs :

[hardware detail & software versions on the bottom]

- creating a snapshot with lvcreate -L 10G -n my_backup -s 
/dev/myvg/xfs_storage is OK without using xfs_freeze.

- BUT lvremove the "my_backup" LV (snapshot LV) freeze completely the 
snapshotted LV (xfs_storage in this case). Some days after testing this, i 
found that a simple "dmsetup resume myvg-my_backup" unlock the whole thing 
and lvremove completes.

At this point I was happy to add/remove snapshots freely (but have not tried 
to make multiple snapshot, which kills performances), but now i have a 
snapshot, i can't mount it... here is the scenario :

- lvcreate as shown above
- mount -o nouuid /dev/myvg/my_backup /backups/snapshot

syslog says :
Apr 22 15:14:47 filer1 kernel: XFS mounting filesystem dm-2
Apr 22 15:14:48 filer1 kernel: Starting XFS recovery on filesystem: dm-2 
(logdev: internal)

and nothing else. The I/O activity shown by iostat is the same (no increase 
due to a real XFS recovery)
trying mount -o nouuid,ro does the same. when strace-ing the mount command, 
the last lines are :
open("/dev/myvg/my_backup", O_RDONLY) = 3
lseek(3, 0, SEEK_SET) = 0
read(3, "XFSB\0\0\20\0\0\0\0\0\4\260\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 576) = 
576
close(3) = 0
mount("/dev/myvg/my_backup", "/backups/snapshot/", "xfs", 
MS_RDONLY|0xc0ed0000, 0x517b60 <unfinished ...>

now, i can't kill the mount command initiated neither soft reboot the 
server. I only want to create a snapshot to xfsdump - it , xfsrestore it on 
another backup server, then delete the snapshot.

Does someone here get the same problems ?

Hardware detail:
RAID 10 with 64K stripe on a
3ware 9500S-12 controller and 12x250GB
system is not installed on the LVM (separate RAID 1)

Software versions:
Linux kernel 2.6.16.1
LVM & mapper version 2.01.15 (library 1.01.15, driver version 4.5.0)
XFS utils version 2.7.11
no patches applied, all tools compiled from the official sources

LVM config :
1 VG created from 1 PV (the RAID array is known to the system by /dev/sdb)
some LVs. the LV sizes i want to snapshot are ~200GB each.

-- 
Gabriel Barazer <gabriel@oxeva.fr>
OXEVA 

Re: [linux-lvm] Another XFS + LVM2 snapshots problems

[Alasdair G Kergon]

On Sat, Apr 22, 2006 at 04:13:01PM +0200, Gabriel Barazer wrote:
> Linux kernel 2.6.16.1
> LVM & mapper version 2.01.15 (library 1.01.15, driver version 4.5.0)

As you discovered, those versions are not compatible.
You upgraded your kernel to a recent one: you need to upgrade your 
dm & lvm2 packages to correspond with that kernel.  (1.02.* & 2.02.*)

Alasdair
-- 
agk@redhat.com

Re: [linux-lvm] Another XFS + LVM2 snapshots problems

[Luca Berra]

On Sat, Apr 22, 2006 at 07:01:04PM +0100, Alasdair G Kergon wrote:
>On Sat, Apr 22, 2006 at 04:13:01PM +0200, Gabriel Barazer wrote:
>> Linux kernel 2.6.16.1
>> LVM & mapper version 2.01.15 (library 1.01.15, driver version 4.5.0)
>
>As you discovered, those versions are not compatible.
>You upgraded your kernel to a recent one: you need to upgrade your 
>dm & lvm2 packages to correspond with that kernel.  (1.02.* & 2.02.*)
>
sorry,
is there a documented compatibility matrix between dm driver version and
device-mapper library version?

Regards,
L.

-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
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Re: [linux-lvm] Another XFS + LVM2 snapshots problems

[Alasdair G Kergon]

On Sat, Apr 22, 2006 at 09:56:44PM +0200, Luca Berra wrote:
> is there a documented compatibility matrix between dm driver version and
> device-mapper library version?
 
The general rule is that the version of libdevmapper should be at
least as new as the latest one available at the time when the upstream
kernel you're using was released.  And lvm2 should normally be at
least as new as libdevmapper.

In brief, new libdevmappers will normally work with older kernels, but
new kernels won't necessarily work with older libdevmappers, though
incompatibilities are rare.  When possible, we add support for kernel
changes to the userspace tools some time before the features
themselves hit the upstream kernel to allow time for the new tools to
propagate.  (A current example is dm mirror block_on_error support.)

Alasdair
-- 
agk@redhat.com