Xen users - Sep 2007 - Best practice for presenting disk to (HVM) RHEL DomUs?

I have an existing RHEL4 DomU here that I''d like to present some extra
to.  An extra pair or 146G SCSI drives have been made available in the
Dom0, and I''m trying to work out how best to present them entirely to
a single DomU.

Ultimately I want the disks to be setup as a Software mirror and
mkfs''d into a single ~140GB partition.  Can people recommend the best
way to do this to yield good I/O performance?

I''m not sure whether I should make the software mirror on the Dom0 and
then present /dev/mdX to the DomU (assuming this is possible).  Or
should I just present the raw disks straight to the DomU and let the
DomU handle the mirroring?

As a first stab at this, what I''ve done is the latter and configured
things like this:

    disk = [ ''file:/var/lib/xen/images/domu.img,hda,w'',
             ''phy:/dev/sdd,ioemu:hdb,w'',
	     ''phy:/dev/sde,ioemu:hdc,w'' ]

.. then on the DomU, run:

    mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hdb1 /dev/hdc1
    mkfs.ext3 /dev/md0

I''m not sure that this is best (or fastest, it seems quite slow) - any
suggestions?

Dom0 is RHEL5 (64-bit).  DomU is RHEL4 (64-bit), HVM virtualized.

Cheers,

Robert.

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

On Mon, Sep 24, 2007 at 05:43:26PM +1000, Robert Sturrock
wrote:
>
> [HVM] 
> I have an existing RHEL4 DomU here that I''d like to present some
extra
> to.  An extra pair or 146G SCSI drives have been made available in the
> Dom0, and I''m trying to work out how best to present them entirely
to
> a single DomU.
> 
> Ultimately I want the disks to be setup as a Software mirror and
> mkfs''d into a single ~140GB partition.  Can people recommend the
best
> way to do this to yield good I/O performance?
> 
> I''m not sure whether I should make the software mirror on the Dom0
and
> then present /dev/mdX to the DomU (assuming this is possible).  Or
> should I just present the raw disks straight to the DomU and let the
> DomU handle the mirroring?
Presenting the two disks to the HVM-domU and making the raid1 in the
domU will to my understanding double the i/o that the qemu-device-
emulation hast to handle.
Placing the raid1-operation in the dom0 will do it there and the data
has to travel only once into the domU.

If the domU was paravirtualized i wouldnt be sure if the dom0 can
handle the raid1 faster than the domU.


Christian

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users