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Re: AW: [Xen-users] Best way to use iSCSI in domU

Rustedt, Florian wrote:

That depends on your scenario. If you've got more than one dom0(Xen-Servers), exspecially for redundancy, then it's not a good idea to make dom0 the iscsi-host.

Of course, you can connect to any iscsi-target directly from the domUs, as you can connect the dom0 vias iscsi and share the ressource via NFS p.e. then.

Me personally, i would connect it directly to the domUs, as this is straightforward.

Much what I thought - attach directly from the DomU and then the connection is portable wherever you host that DomU. It didn't work well for me (see below).

Why are you thinking about implementing another "hop" via dom0? What is the advantage you asume in this case?

Performance !
I'm not alone in finding iSCSI performance was "rather poor" connecting from the DomU. I reluctantly configured iSCSI in the Dom0 and passed the resulting SCSI device as a block device to the DomU and performance was "quite acceptable". From bits I've picked up here and there, I believe it's something to do with the network stack in XEN/Dom0 being single threaded and killing performance - though I don't know why it should affect iSCSI and not other networking.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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