Hey everyone, recently I Ran into an issue where an iSCSI datastore became disconnected from one of my ESX Hosts. All other hosts could see them fine. The datastores reside on an HP All-in-One Storage Server. Once of the most important things to do is first check physical connections to the iSCSI network, if you have it VLAN’d that way. Second goto the service console, be it directly or using the VMCLI(VMware Command Line Interface) and see if the vmkernel port assigned to you ESX host can ping the iSCSI target host, the command is vmkping. VMkping will send a ping request solely from the vmkernel port to the iSCSI target. If the communication is working OK, then you know its the Windows host. I had to go into the HP Aio and remove the iSCSI target and re-add it, make sure you document all settings! Once that was done, I ran a rescan on the configure>storage tab and I was good to go. Another quick way to see that the host is having errors is hitting F12 on an ESX Host, this will show you a multitude of information that you don’t necessarily need, but it will also show you the most recent errors as well. Good Luck!