I have done a considerable amount of searching on this and while I have found a lot of people with very similar needs, none quite seem to match up with mine. First of all, this computer is used almost solely for editing photos in my wife's photography business. The specs currently are: 27" late 2011 iMac Core i5 2.7ghz quad radeon 6790m gpu 20GB total memory (2x8gb + the 2x2gb that shipped with the machine) OCZ Vertex 3 240GB SSD installed internally in the extra SATA port 1 TB HDD (original from mac) As you can tell, I have started to upgrade the machine to perform better for my wife's business. Currently, the OS and apps are on the SSD and I have the 1TB HDD with everything else on it. My question has to do with the location of the scratch disk, her active file storage and backup storage drives. Ideally, I would have 3 internal drives, one for OS + Apps, one for scratch and one for active files. I understand that it is important to spread the load across all three to optimize performance, however, my internal SSD drive is quite a bit faster than the internal HDD and lightyears faster than an external usb or firewire drive. Due to the fact that she wants to keep her internal DVD drive operational, I cannot install another internal or make an external SATA drive. So, what is the best way to handle all of this without blowing a fortune on external thunderbolt storage? I purchased the 2x8GB of ram because I had hoped to install the full 32GB and use about half of it as a scratch disk but now I have learned that the scratch needs to be about 1/3 the total system memory or 11GB. Is that large enough? I have not been able to evaluate her scratch usage because she has not changed her process to take advantage of the new machine yet, she doesn't do any panorama work but she some of her steps would improve if she could open quite a few files at once, (15-30). Also, is there any advantage to using a ram disk for scratch if the OS X unified buffer will store the scratch in the ram anyway? I have already noticed her 20GB maxed (including inactive memory) does that mean that it is caching her current scratch? Where is the best location for her scratch and active files with the drives I have installed? I have been using her 1TB for active files and scratch and the SSD for OS and apps, is this best or would things speed up if I moved one of those over to the SSD? Would I notice a big enough speed increase to justify the purchase of external thunderbolt storage? I don't like the cost of these add-ons but if the performance will be increased substantially, I will go ahead and pursue it. Lastly, what do you believe is the best way to handle back-up storage? I had been thinking about using a 4 drive raid enclosure filled 3TB HDD's for 6TB of total storage, is firewire fast enough or should I find a way to make thunderbolt/eSATA work? My dream setup would be to purchase the LaCie Thunderbolt to eSATA adapter and attach a large eSATA raid enclosure for backup and then daisychain this to the seagate thunderbolt to eSATA 2.5" adapter with an SSD attached for the scratch disk. However, this arrangement will cost over 1k and I'd rather not spend that much if I can help it.