I've been intrigued by iSCSI for some time now. I currently have a [ReadyNAS Pro](http://www.netgear.com/Products/Storage/ReadyNASPro.aspx) with 6.5TB of usable, redundant storage space. Today, I created a 20GB iSCSI volume on the ReadyNAS Pro and used [globalSAN](http://www.studionetworksolutions.com/products/product_detail.php?t=more&pi=11) to initiate a connection from my Mac Pro (partitioned and formatted using HFS+ Journaled). I copied 10GB of Canon 5D Mark II RAW files to the volume and imported the images into a Lightroom library (stored on my local file system). After using the library for a little while, I have concluded that I cannot tell the difference in speed between storing my images locally and on an iSCSI volume on the ReadyNAS Pro. In theory, I could store my entire RAW image archive on the NAS box and work off of the network.
There are two issues stopping me from going with this set up:
1. I'd have to set up an additional NAS box to back up the working NAS box. I'm too paranoid to be comfortable with storing files on only one machine, even if it uses a RAID.
2. The ReadyNAS' maximum iSCSI volume size is 2TB. I don't like managing multiple volumes, and would rather have a single large volume.
At the moment, my Mac Pro contains two 4TB data volumes plus SSD boot and swap disks. [Crashplan](http://crashplan.com) continuously backs up my data volume to the NAS, and each night, the data volume is automatically synchronized to the local backup volume (that's three copies, locally).
Since I'm about to exceed the capacity of my current (local) 4TB data partition, I may end up just changing my RAID configuration to a single 8TB stripe, which would be backed up to my NAS box over gigabit (traditional share -- not iSCSI). Having good backups makes me feel secure using a 4-disk stripe, and since I'm starting to do more video work, the local speed boost would be useful.
In any case, it's good to know that iSCSI is an option for the future -- it's certainly less expensive and complicated than setting up a SAN over Fibre Channel (which I'm wired for). When the ReadyNAS supports >2TB iSCSI volumes, I may go that route.