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

[henry ritzlmayr <xen-list@xxxxxx>]

Am Montag, den 08.09.2008, 10:09 -0400 schrieb Ross S. W. Walker:
> 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

Hi Ross, 

thanks for the reply, I will give this a shot. Do you have any
information (link) on why the md raid10 driver is "a little off" or
any information if there are any plans to change this. I guess this 
is probably an upstream issue, but on some test systems I only have
three disks so the above solution works only for a subset of my
machines.

Henry 



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