I can't remember I will ask our resident brain tomoz as I know he had this loads of times- poor old bold g*t

Scan the hosts by right-clicking each HBA (select scan) in each host. I do. Even after applying a patch that seems to have fixed the issue. I just find it to be a 'sure thing' when I scan on each host's HBA directly. Sometimes I have to do that TWICE per HBA. You can also resort to cmd line scanning, but many folks prefer the gui, and you don't have to connect to each and every ESX host when you use VC of course, versus your favorite SSH client for the cmd line stuff.

Anyway, in the end, I prefer the right-click-each-HBA and scan approach. It works. I'm going to 3.5 soon and will be scanning galore(!) in my dev environment to see if it's 'safe' to go back to the Rescan dialog box (with those checkboxes). Until then, I'm set in my safe ways.

That seems like an awful lot of work(around) just to get your HBA's re-scanned. I have some suggested reading for you. You are NOT alone in your problem, but there are solutions herein:

http://communities.vmware.com/thread/67309

In particular (and because I don't want you to have to wade through the NUMEROUS pages of this thread where a bunch of us posted our experiences/woes/frustrations while this issue, you'll be interested in this: http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&externalId=10229

In the end, I do believe the patch made it into 3.0.2 but I had put the patch onto my 3.0.1 hosts (and subsequently upgraded to 3.0.2) and have not had the problem since.

But--ha--out of sheer paranoia I STILL rescan my HBA's one at a time (right click on HBA, select 'Rescan'). Half the time, I have to do this a SECOND time for the new LUN/s to be recognized.