So I got open-iscsi working on debian, in so much that I had four disks, two to the preferred controller were good but the two to the second controller werent. Switching the preferred controller
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After installing multipath-tools I started looking at dmsetup but the target types listed in the man page: linear, striped and error, didnt make sense. When I read the INTRO file included in the debian package I saw there were additional types snapshot and mirror. This thread clued me in to there being a multipath type.