I was monitoring my system, so I knew the file was /dev/sdb was the new iSCSI target I was trying to turn into a file system. TO provide it, I ran:
iscsiadm -m session --print=3
... scsi4 Channel 00 Id 0 Lun: 0 scsi4 Channel 00 Id 0 Lun: 1 Attached scsi disk sdb State: running
But what did that do? Using Strace helped me sort it a little. I worked backwards.