iSCSI Dynamic Disks Don't Reactivate At Boot Time
If you are using the Microsoft iSCSI software initiator and you define a iSCSI disk as "Dynamic", it won't re-activate when the system is rebooted. You must manually activate it.
If you want it to activate on boot, you must convert the disk to Basic. (Of course you will lose all data off this disk when you make the conversion.) Then re-partition and re-format.