Re: Weird Issue with raid 5+0

[chris <tknchris@gmail.com>]

That is exactly what I didn't want to hear :( I am running
2.6.26-2-xen-amd64. Are you sure its a kernel problem and nothing to
do with my chunk/block sizes? If this is a bug what versions are
affected, I'll build a new domU kernel and see if I can get it working
there.

- chris

On Sun, Feb 21, 2010 at 12:48 AM, Neil Brown <neilb@suse.de> wrote:
> On Sat, 20 Feb 2010 23:33:23 -0500
> chris <tknchris@gmail.com> wrote:
>
>> Hello,
>>
>> I am trying to setup a raid 5+0 on 6 1TB sata disks. I created the
>> arrays like so:
>>
>> mdadm --create /dev/md2 --level=5 --raid-devices=2 /dev/sda /dev/sdb /dev/sdc
>> mdadm --create /dev/md3 --level=5 --raid-devices=2 /dev/sdd /dev/sde /dev/sdf
>> mdadm --create /dev/md4 --level=0 --raid-devices=2 /dev/md2 /dev/md3
>>
>> The arrays create and sync fine, then I put lvm on top and create a
>> volume group and everything seems fine. I created 2 logical volumes
>> and formatted them with filesystems and initially didn't realize
>> anything was wrong. After running 2 virtual machines on them for a
>> while  I noticed the vm's were reporting bad blocks on the volume. I
>> looked in the dom0 dmesg and found tons of messages such as:
>>
>> [444905.674655] raid0_make_request bug: can't convert block across
>> chunks or bigger than 64k 69314431 4
>
> 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
>
>
>>
>> Chunksize for both raid5's and the raid0 is 64k so it would appear the
>> issue is not that the chunk size is greater than 64k. I also find it
>> hard to believe it could be any kind of lvm issue simply because the
>> message in dmesg clearly shows its related to the raid0.
>>
>> Any ideas on what I'm missing here would be greatly appreciated. I
>> would imagine it is some kind of alignment between block and chunk
>> sizes but I can't seem to figure it out :)
>>
>> More detailed information including raid information and errors is at
>> http://pastebin.com/f6a52db74
>>
>> - chris
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