How to troubleshoot when Windows Server 2012 R2 connected to SAN via iSCSI fails to attach and mount the LUNs from the iSCSI target
I would at first look at the availability of the SAN from the Windows Server. Any possible firewalls that could block the connections Then I would look into Windows Event Viewer to find iSCSI initiator log entries and see if there are any errors occurring.
Also, I'd like to have more information on the problem. E.g. How does the failure in Windows 2012 look? Are there any errors? What is the iSCSI target device etc