We are running two VMware ESXi v4 systems. We access our VMs on a NAS via iSCSI. Recently, we had some issues and had to remove and reconfigure the iSCSI LUN on each server. On one, it came right up. We were able to see the LUN and it mounted just fine and we saw all of our VMs. On the second VMware ESXi box, if we do a Rescan.. it won't auto-mount the LUN (which has VMFS). If we do an Add Storage, we can find the LUN but then we get only the option "Format the disk [create a new datastore]).
Obviously that would be a bad idea. :)
I can't figure out the problem.
BTW, we can mount a second LUN on both VMware servers just fine that we use for some other VMs that we just created.