I'm being thick, I'm sure.

How do I find which disk volumes are on which iSCSI devices?

The iSCSI Initiator lists targets, their MAC and IP addresses. It also list volumes but not which traget they're on.

The Disk Manager will give a target ID in the properties for each disk.

How do I match the two?

I need to perform maintenance on one iSCSI device, so I need to copy its contents to the other as backup.