We just had a Citrix XEN issue that others may be able to comment on.
It seems (according to the Citrix engineer) the UUID of an iSCSI vol/LUN associated with a XEN Storage Repository changed when we did a DSS v5 to v6 upgrade, causing XEN to loose connection with the LVM data that was on that LUN. We may have then compounded the problem by detaching, then failing that, "forgetting" & recreating the SR definition, in an attempt to sort it. We thought also that IETD vs SCST may have been the issue, but we eliminated that. (another possible complicating factor may have been adding a v6 demo product key, which seems to scap the setup & config data, requiring it to be reloaded again.)

The the Citrix engineer was able to do his Linux magic & correct the LVM data for the SR, pointing it to the new UUID, and saved the day (well, late night/s actually!).

Anyway,
(a) should the UUIDs of volumes change across version upgrades?
(b) how does we make sure this doesn't happen again?
From the XEN docs, we should have been able to detach & re-attach the SR, even if we have moved the LUN to a different location.
(note that the UUID is different from the SCSI ID, which is associated with just the ISCS target. Both strings were in the /iscsi/target001.conf file in DSS, but I am not clear which are stored/preserved in the setup/config data file). Cheers.