Re: [Xen-users] iSCSI target - run in Dom0 or DomU?

[Thomas Harold <tgh@xxxxxxxxxxxx>]

Lucas Santos wrote:
> Thomas Harold wrote:
>
> > The test unit is an AMD Athlon64 X2 4200+ AM2 socket, 2GB RAM, and
> > multiple SATA drives.  Since it has the AM2 socket, I believe that it
> > supports AMD-V (AMD's virtual technology) so we should be able to run
> > unmodified guest OSs on it.  Any guest OSs besides the iSCSI/SAN
> > specific tasks will eventually be migrated off to an external box
> > (either new SocketF Opteron systems or AM2 Athlon64 systems).
> Very nice hardware!
Thanks, It's a start for testing. :)  Still waiting to see what Socket F 
Opteron prices are going to be.  We may go with AM2 motherboards that 
take ECC memory in order to get more Xen head units (spread the load and 
risk over multiple physical units).
> > My plan for the disks is to lay software RAID over the disks (RAID1 for
> > the first pair, RAID10 for the second set of 6 disks).  Then lay LVM on
> > top of mdadm's software RAID before handing it off to iscsitarget to be
> > divided up for use by the iSCSI initiators.
> Can't you do RAID inside the disk controllers? It's much better than
> software hardware (with real raid controllers).
I'm actually much more comfortable with Software RAID (and mdadm).  I 
find it to be flexible and performance is good enough for most cases. 
For instance, since this test unit is going to have 14 HDs, there's a 
good chance that the hotspare for arrays will have to be on another 
controller.
We're doing RAID1 on 2-drives at the start of the drive set.  Then 
eventually a 4-drive RAID10 and a 6-drive RAID10 with 2 hot spares 
sitting at the end of the drive set.  But that's a topic for a SAN 
mailing list (grin).
> > Specific questions:
> >
> > 1) The mdadm and LVM will need to happen in Dom0?
> Yes, it should be in the dom0.
>
> > 2) Should iscsitarget also run in Dom0 or should it be moved into a DomU?
> Will you use iscsi to export volumes to be used for domU, right? So, it
> have to be done by dom0.
Thanks for the info.

> > 3) I assume that ethernet card bonding should happen in Dom0 with the
> > bonded interface presented as a virtual interface to the DomUs?
> I tried some time ago do bounding in dom0, but it didn't work. Probable
> was my fault.
We'll see how bonding goes... first time trying it in Linux.  But we 
picked up an inexpensive SMC 16/24 port switch that allows link 
aggregation (along with jumbo frames).  The SMC switch was about $250 
and will work well enough for testing.
...

Worst come to worst, I take Xen back off the box.  But since it's an AM2 
box, it's worth trying to see how AMD-V performs.
(Also thanks to Ed and Jason for their replies.)

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