sorry I missed this post op here is what you can do with a lacie
note this is no longer for sale but has just about all the info you need.
http://www.ebay.com/itm/15070469033...X:IT&_trksid=p3984.m1560.l2649#ht_3084wt_1131
here is my mac rumors thread on it
https://forums.macrumors.com/threads/1280118/
As far as I know I am the only person that has done this and posted and no one else is qualified to tell you what to expect from it. It works fine and the lacie is fine and it can work fanless. I like it so much that when the item did not sell on ebay I kept it. In fact I am using it right now.
I really advise samsung ssd's if you do this. as they pull the least power. each drive will max a Sata II so samsung series 470 which are sata II are fine.
you can run them as raid0 for max speed
raid1 for safe but slow each drive will max as a Sata II due to the internal bridge
and even jbod. In fact if you use your iMac for business and run an internal ssd you risk it dying and being stuck. if you use a lacie and make a back up copy on the internal and the lacie dies you can use the internal hdd to run your work. The power supply is so so but I gave a link on my thread for a perfectly fine power supply on ebay. Same connector and made by the same power supply company.