On Mon, Mar 19, 2012 at 01:35:19PM +1100, Virgil wrote:
> I'm having a problem with mdraid running in a DomU. The issue is that mdraid 
> declares one leg of the raid to have failed (when there's actually nothing 
> wrong).
> 
> DomU is fc16 - 3.2.2-1.fc16.x86_64
> Dom0 is fc14 - 2.6.32.26-174.2.xendom0.fc12.x86_64
> 
> The same DomU running on Dom0 fc16 - 3.2.7-1.fc16.x86_64 runs perfectly.
> 
> This appears to be a known issue, however the resolution (which seems to be 
> to 
> disable barriers on the fly) doesn't seem to work in this case.

hm, that is true - it wouldn't as the workarounds are for filesystems.

But perhaps - is there a way to turn barriers of in the raid system?

> 
> My question is: Is it possible to pass a parameter to the blkfront driver to 
> ask it not to enable barrier during initialization? or is there another work 
> around?

Not that I know of. You could back-port the proper fix to 2.6.32
(or just "Fix" the older 2.6.32 to not advetise feature-barrier).

> 
> [    1.033058] blkfront: xvda: barrier: enabled
> [    1.099153]  xvda: xvda1 xvda2
> [    1.102871] blkfront: xvdb: barrier: enabled
> [    1.130876]  xvdb: xvdb1 xvdb2
> [    1.292692] md: bind<xvdb1>
> [    1.413416] md: bind<xvda1>
> [    1.419411] md: raid1 personality registered for level 1
> [    1.419836] bio: create slab <bio-1> at 1
> [    1.419953] md/raid1:md127: active with 2 out of 2 mirrors
> [    1.419992] md127: detected capacity change from 0 to 7516180480
> [    1.424562]  md127: unknown partition table
> [    1.547284] EXT4-fs (md127): barriers disabled
> [    1.553107] EXT4-fs (md127): mounted filesystem with ordered data mode. 
> Opts: (null)
> [    1.669483] dracut: Checking ext4: /dev/disk/by-label/rootfs
> [    1.669592] dracut: issuing e2fsck -a  /dev/disk/by-label/rootfs
> [    1.690595] blkfront: barrier: empty write xvdb op failed
> [    1.690611] blkfront: xvdb: barrier or flush: disabled
> [    1.690628] end_request: I/O error, dev xvdb, sector 14682096
> [    1.690638] end_request: I/O error, dev xvdb, sector 14682096
> [    1.690646] md: super_written gets error=-5, uptodate=0
> [    1.690655] md/raid1:md127: Disk failure on xvdb1, disabling device.
> [    1.690657] md/raid1:md127: Operation continuing on 1 devices.
> [    1.690677] blkfront: barrier: empty write xvda op failed
> [    1.690684] blkfront: xvda: barrier or flush: disabled
> [    1.690696] end_request: I/O error, dev xvda, sector 14682096
> [    1.690705] end_request: I/O error, dev xvda, sector 14682096
> [    1.690713] md: super_written gets error=-5, uptodate=0
> [    1.692991] RAID1 conf printout:
> [    1.692997]  --- wd:1 rd:2
> [    1.693002]  disk 0, wo:0, o:1, dev:xvda1
> [    1.693006]  disk 1, wo:1, o:0, dev:xvdb1
> [    1.693010] RAID1 conf printout:
> [    1.693013]  --- wd:1 rd:2
> [    1.693016]  disk 0, wo:0, o:1, dev:xvda1
> [    1.702896] dracut: rootfs: clean, 25635/454272 files, 293967/1835005 
> blocks
> [    1.703682] dracut: Remounting /dev/disk/by-label/rootfs with -o ro
> [    1.773347] EXT4-fs (md127): barriers disabled
> [    1.774552] EXT4-fs (md127): mounted filesystem with ordered data mode. 
> Opts: (null)
> [    1.797159] dracut: Mounted root filesystem /dev/md127
> [    1.937620] dracut: Switching root
> 
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