[Xen-users] Raid 5+0 Problems Under Xen

[chris <tknchris@xxxxxxxxx>]

I am experiencing a weird issue with a raid 5+0 under dom0. I am
running xen 3.2 from debian lenny which has the 2.6.26-2-xen-amd64
dom0 kernel. There are 6 1TB sata disks which are arranged in 2 sets
of 3 disk raid5's which are raid0'd together. Chunk size on all arrays
is 64k and I was able to create and sync all arrays with no issues,
then initialized lvm on the raid0 and created 2 lv's all with no
issues. I was able to install 2 guests with no apparent problems
however after 2 days I noticed errors in the guests that their disks
had bad blocks. I checked dom0 and noticed lots of messages like
these:

[305012.467758] raid0_make_request bug: can't convert block across
chunks or bigger than 64k 2385277 4

I have posted this to linux-raid mailinglist where they have indicated
that this bug is likely due to xenified kernel.

A quote from the linux-raid mailinglist:

> This looks like a bug in 'dm' or more likely xen.
> Assuming you are using a recent kernel (you didn't say), raid0 is
> receiving a request that does not fit entirely in on chunk, and
> which has more than on page in the bi_iovec.
> i.e. bi_vcnt != 1 or bi_idx != 0.
>
> As raid0 has a merge_bvec_fn, dm should not be sending bios with more than 1
> page without first cheking that the merge_bvec_fn accepts the extra page.
> But the raid0 merge_bvec_fn will reject any bio which does not fit in
> a chunk.
>
> dm-linear appears to honour the merge_bvec_fn of the underlying device
> in the implementation of its own merge_bvec_fn.  So presumably the xen client
> is not making the appropriate merge_bvec_fn call.
> I am not very familiar with xen:  how exactly are you making the logical
> volume available to xen?
> Also, what kernel are you running?
>
> NeilBrown

Unfortunately since I am running 3.2 from what I understand there are
limited dom0 options, so I am not sure if there is any advice on this
mailinglist or if I should bring this up on xen-devel. I have detailed
raid information and errors at http://pastebin.com/f6a52db74

I would appreciate any advice or input on this issue.

- chris

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