iSCSI – Managing Multiple Initiators for the Same LUN

Xen has a built-in locking mechanism that should be used, especially if using hot or live migration. We have a NFS share mounted on all of our Dom0 hosts, and Xen checks there first to see if someone else is running an instance of a DomU before attempting to start it.

Look in your xend-config.sxp file -- the config settings your looking for start at about line 261 on my system, and are called xend-domain-lock, xend-domain-lock-path, and if you want to set up an external utility to manage it in another way, you can specify an external command to run with xend-domain-lock-utility. I'm using Xen 3.3.1 on SLES11; your mileage may vary.

We manage xend, xendomains, and nfs with pacemaker/openais, and store the lock files on an NFS mount that is made highly available by means of pacemaker and a partition on the san.

You can't do this sorry, not with v4 as it's a limitation of SCSI-2/VMFS3 (version 5 however changes things a lot ;) ). Just go back and represent your LUNs as 2TB one and extent them if required, you're still limited to 2TB vmdk's anyway so it's a little pointless doing extent'ed DS's anyway really. If it's any consolation I limit my DS's to 500GB anyway to ensure the ops people don't over subscribe any given DS with VMs.