I haven't tested iSCSI, but I noticed on my Beta3 setup that there is no swap file space at all - a drastic change from 2GB per disk in the previous versions (Beta2 and earlier). I setup a ZFS RAIDZ2 with forced 4k sectors, but otherwise nothing special. Not sure if no swap space is a bug or if it's a change in how it's being designed.
Do you have swap space on your config? Maybe you have the same problem(?) I have?