From last post of ESXi 5.5 Help,
I created a few VMs, and allowed them to run for about 5 days, on the 6th day, this is what happen.
I remove the iSCSI from esxi, then add them back, it can see all 3 LUN on the one target, with 2 path each.
I don't use software iSCSI, I have hardware iSCSI.
Only the ISODisk lun was working, and was the only one without L2 cache, So I deleted the VMDisk & FileDisk and recreated them without L2 cache.
Under the datastore tab it says it can't mount the lun, but under the devices tab it says that they are mounted.
http://i40.tinypic.com/14lm0r5.jpg