This is a process I have tested over and over...with mixed results...
I have 2 x DSS 6 systems running with iSCSI auto-failover in a vSphere 4 environment. I have had to upgrade these systems 3 times.
DSS 5 to DSS 6 beta
DSS 6 beta to DSS 6 up4
DSS 6 up4 to DSS 6 up6 (only half way completed).
I will tell you this...it hasn't always been as smooth as I would have liked it. The procedure I use it similar to what Todd has layed out. However, some of the issues I have encountered have been uncommon.
The secondary server is always the easiest. Just save config, reboot, install and reload config. After the second reboot you can restart the failover service and all is well.
Upgrading the primary has been cumbersome for me and also fatal at times. I've corrupted 2 vmware active directory servers and a couple misc servers because of downtime. I will say this...this has always been going from a beta version to a final version so this isn't a true estimate.
When upgrading the primary server start the failover to the secondary and reboot, install, reload, etc. Here's where it gets tricky. When I have tried to failback all must be well otherwise it will go belly up trying to failback and my iscsi failover service will stop all together which disconnects all 7 of my ESX servers...not good!
Some of the issues I have had are related to NIC renumbering, defaulting back to 1500 MTU size, and also even switching back to IETD iscsi. I'll say this again...this was beta versions of DSS 6.
I did update my secondary server last night to update 6 and it was about as smooth as it could be. I am going to try the primary server today after I finish storage vmotioning my critical virtual machines to a holdover iscsi. I will post the update on how it went. Keep in mind this is a full DSS v6 up4 to v6 update so there should be no surprises.
Please feel free to contact me if you have any questions about this, as I have had to do it many time on a live production system so I have gone through the pains. Keep in mind we also have an EMC Clariion with SSD for a heavy I/O AIX database and the upgrade/hba replacements for that are just as painful so don't think everything should be a point and click and you're done. If it were always this easy...most of us wouldn't have jobs :-) Planning, testing, planning, and testing can be your best friend for these procedures. Of course the beauty of VMware is storage vmotion. Setup a simple DSS lite iscsi target and move your production servers off the main san while your're upgrading...without downtime!
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