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Re: [Xen-users] Xen and iSCSI


Am Samstag, 28. Januar 2006 18:48 schrieb Javier Guerra:
> On Saturday 28 January 2006 11:24 am, Markus Hochholdinger wrote:
> > has anyone experience with the use of iscsi (as iscsi initiator) in Xen
> > (which Xen version?). Does it work in dom0 and domU?
> i haven't tried it, but i guess performance wouldn't be as good.  iSCSI is
> a complex protocol, and t needs a lot of help from the NIC to be
> competitive with other forms of SAN.  that's why you see iSCSI cards from
> Adaptec and Intel.  those cards look like regular SCSI hardware (i think
> the Adaptec cards might even use the same driver for SCSI and iSCSI)

so the cpu has to work a lot for iscsi. But should performance be better in 
dom0 than in domU? I'm planning to use iscsi in domU, if possible.

> under Xen, it's somewhat more complex to get TCP offloading, and i don't
> think you could use iSCSI cards from domU.  the CPU utilization would be
> way higher.

I don't want to use iscsi cards because they are very expensive. How is 
network performance in domU? Is it possible to get almost the throughput of 
the rela nic?

> what i plan to do (once i get a few test boxes) is to use coraid's AoE
> protocol (the driver is in the main Linux tree).  it's designed to be
> software driven, without any special card; and it's CPU utilization seems
> to be around ATA levels.

I also read about this. My thoughts were that iscsi exists longer and is a 
standard. AoE is no standard and can only be used by linux by now (i think). 
You also can make iscsi targets and initiators without any special hardware.

> with any kind of SAN, i think the best strategy would be to use CLVM in
> dom0 and export the logical volumes to the domUs; this way you only have to
> setup the SAN drivers in dom0, the domUs would treat those as local disks.

Is this safe for migration? How can you get the block device, which is 
exported to the domU, to other Xen hosts when migrating an domU? If all could 
take place in domU (iscsi initiator and rootfs on iscsi) you are completly 
independent from the dom0 block device configuration. I would like to prefer 
this if possible and if performance is not to bad.



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