[Xen-users] lvm as raw disk and barriers

[Alexandre Chapellon <a.chapellon@xxxxxxxxx>]

Hello,

I was previously using LVM2 volumes as partitions for my PV guests.
For some reasons I now have to switch to a model where an LV is a raw 
disk and not a partition.
This works flawlessly at first look. But today while searching in dmes 
logs I found the following errors:
##############
...
[    8.515912] EXT4-fs (xvda3): mounted filesystem with ordered data mode
[   12.961268] blkfront: xvda: write barrier op failed
[   12.962398] blkfront: xvda: barriers disabled
[   12.963434] end_request: I/O error, dev xvda, sector 3410072
[   12.964285] end_request: I/O error, dev xvda, sector 3410072
[   12.965438] JBD2: wait_on_commit_record: sync failed on xvda1-8 - 
disabling barriers
[   13.820957] JBD: barrier-based sync failed on xvda3-8 - disabling 
barriers
...
##############

I didn't have any trouble with fs consistency sor far, but I know not 
using barriers is more prone to falling into FS problems (even with 
modern journalised fs).
Why am I getting this issue? is it related to using LV as raw disks? Is 
there anything I can do to re-enable barriers?
Am using Xen 3.2.1 on Debian Lenny system, kernel 2.6.26-2-xen-amd64 as 
dom0, debian squeeze , kernel 2.6.32-5-amd64 as guests. backend storage 
devices are lvm volumes from multipathed FCs SANs.
--
<http://www.horoa.net>

Alexandre Chapellon

Ingénierie des systèmes open sources et réseaux.
Follow me on twitter: @alxgomz <http://www.twitter.com/alxgomz>

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