[Xen-users] blkfront: barrier: empty write op failed

[Luca Lesinigo <luca@xxxxxxxxx>]

I have some Xen systems running Xen-4.1.1, dom0 linux-2.6.38 patched (it's 
gentoo's xen-sources) and domUs running linux-3.0.4 (vanilla sources from 
kernel.org).
Block devices are phy on LVM2 volumes on DRBD-8.3.9 devices.

Not immediately after boot, but after some I/O load on the disks I start seeing 
these in the domUs:
        blkfront: barrier: empty write xvdb1 op failed
        blkfront: xvdb1: barrier or flush: disabled

the systems appear to keep working correctly anyway.

I discovered the thing in domUs with linux-3.0.3 and got the same with -3.0.4, 
with or without cleancache enabled, mounting either an ext3 or an ext4 
filesystem.
The only domU I have running Ubuntu with its kernel 2.6.24-28-xen seems to be 
immune.

Doing something like "dd if=/dev/zero of=/dev/xvdb1" I wasn't able to trigger 
those messages even if I tried some different 'bs=XXX' values.
Doing a single mkfs.ext3 or mkfs.ext4 *will* trigger those message every time.

Is this something I should be worried about?
Should I switch back to an older kernel or change some other setting?

--
Luca Lesinigo
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