RE: [Xen-users] raid10 + lvm + domU NoGo?

["Ross S. W. Walker" <RWalker@xxxxxxxxxxxxx>]

henry ritzlmayr wrote:
> 
> Hi list, 
> 
> I have a fully updated CentOS 5.2 (Dom0+DomU). I wanted to do some
> performance tests with Databases within a DomU (compare raid-levels).
> >From the theoretical point of view raid10 should be best, but I can´t
> even start the DomU when the lv sits on a raid10.  
> 
> The Error I get within Dom0 is (several of those):
> 
> raid10_make_request bug: can't convert block across chunks or bigger
> than 64k 1024000507 3
> 
> The DomU sees the disk just as a defekt one. 
> 
> Changing from phy to tap:aio gets the DomU running but performancewise
> this is not the solution I am seeking. 
> 
> My google vodoo brought up: 
> 
> http://www.issociate.de/board/post/485110/Bug(?)_in_raid10_(ra
> id10,f2_-_lvm2_-_xen).html
> 
> http://www.issociate.de/board/post/423708/raid10_make_request_
> bug:_can't_convert_block_across_chunks_or_bigger_%5B...%5D.html
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=224077
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=223947
> 
> So for me it looks like this is still a NoGo - right?

The kernel md raid10 driver is a little off.

You could try striping LVs across md RAID1 PVs.

Say you have 6 drives, create 3 MD RAID1s, convert them to PVs
(whole disk is fine no need to partition) add them to a volume
group then create the LVs with lvcreate -i 3 ... which will
cause them to stripe across all 3 PVs.

This will provide identical performance to the MD RAID10 and
should work fine with Xen.

-Ross

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