I think its not related to something on the trueNAS side. if you are using iscsi multipath you should be using round-robin , if one of the paths goes down you still have the other path with your information., so no sanlock . unfortunately if you want iscsi mpath on ovirt, its prefered to edit the config by hand and test. also, with multipath, you can tell the os to 'stop using' one of the paths( represented as a disk).
so, for example:
multipath -ll should* be looking like this:
36589cfc000000341111968eacf965e3c dm-17 FreeNAS ,iSCSI Disk
size=50G features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=0 status=enabled
|- 31:0:0:5 sdl 8:176 failed faulty running
|- 32:0:0:5 sdm 8:192 failed faulty running
|- 35:0:0:5 sdo 8:224 failed faulty running
`- 34:0:0:5 sdn 8:208 failed faulty running
(yes, they are different ones, I wont disconnect one path just to show an example =) )
hope I clarified a bit.