Re: [Xen-users] Xen Disk I/O performance vs native performance: Xen I/O is definitely super super super slow

[John Madden <jmadden@xxxxxxxxxxx>]

On Sun, 2008-01-27 at 15:05 +0100, Sami Dalouche wrote:
> On the one side, it seems that Xen, when used on top of a raid array,
> is
> wayyy slower, but when used on top a plain old disk, seems to be
> pretty
> much native performance. Is there a potential link between Xen and
> RAID
> vs non raid performance ? Or maybe the problem is caused by Xen + RAID
> +
> LVM ?

Unless we're talking software raid here, I don't see the connection.
I'm still concerned about memory sizes here -- you're running the
benchmark with different write sizes based on your differing memory
sizes.  Can we shore that up?  Limit your dom0 to 512MB of memory and
create a domU with 512 MB memory.  Create a RAID device and LVM it if
you want, then mount it in dom0, run `bonnie++ -u root -r 512`, then
umount and export it to domU, mount it there, and run the same
benchmark.  (Note that in neither case is the device the root
filesystem.)

With bonnie++, dd, etc., I've always seen near-native performance
between dom0 and domU.

John




-- 
John Madden
Sr. UNIX Systems Engineer
Ivy Tech Community College of Indiana
jmadden@xxxxxxxxxxx


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