Thanks for your suggestions Manu. They are indeed all iSCSI LUNS
It appears that all iSCSI sessions are logged in:
iscsiadm -m session -P 1
Target: iqn.2005-10.org.freenas.ctl:proxiscsi (non-flash)
Current Portal: 10.4.132.60:3260,257
Persistent Portal: 10.4.132.60:3260,257...