Using a Nexenta VM it is possible to create a 500 TB thin provisioned iSCSI target in three lines:

zpool create zfspool01 raidz c2t0d0 c2t1d0 c2t2d0
zfs create -s -V 500TB zfspool01/share01
zfs set shareiscsi=on zfspool01/share01

In this case the disks c2t0d0, c2t1d0 and c2t2d0 are all dynamic 10 GB virtual disks. This can easily be mounted with the Microsoft iSCSI Initiator for testing; it will be interesting to see how well this plays with ESX…