I've been doing some pretty intensive research down here with iSCSI setups of various kinds. This market segment was a little rough a year ago…but it's much better now. Though there are still no "official" OS X Server setups that support it….certainly not Xsan (too bad!)
read on for a few more iSCSI notes…I've tested both the $130 ATTO iSCSI initiator, and the free one from globalSAN. Both seem to work fine, I could detect no difference in reliability. This was after several days of pounding huge files across both to a rack-mount iSCSI box from StorMagic (a company that really tries to be Mac-friendly, btw)
I've run two absolutely mission-critical apps across iSCSI links for the past week…just to be sure. The performance is much better than the NAS links I'd been using previously.
I like the globalSAN's integration as a control panel, and the nicer interface. But it's not supported, whereas the ATTO one is. The call is probably up to you….both worked well in testing.
I also tested ATTO's iPBridge, a very low-cost way to get old Ultra-3 SCSI raid units back in service over iSCSI. The interface was ugly, but once I read the docs and got it set up, it's worked flawlessly. I added 4TB of storage to my backup server for 500 bucks…hard to beat that. Since it all runs over IP, I can park a unit at another site and have remote backup very easily.
My backup server (Retrospect) couldn't seem to hold a reliable connection to the iscsi mounts until I added another gig-ethernet card and dedicated it to that task. After that, it was fine.
SO…in conclusion, with all the inexpensive iSCSI RAID boxes out there, if you need more storage, it's worth your consideration. Unless you really need FC for some reason (super-performance, or Xsan), I would say go for it. Take the time to read the iSCSI documentation and familiarize yourself with the terminology.