Yes, you can create a fusion drive on older Macs, described in full length here:
- You obviously need both an SSD and a HD. Let's assume they are known to the OS as disk1 and disk7. You can check disk id by
diskutil list
.
diskutil cs create bla disk1 disk7
to create it, where bla
is the name you give to the fusion drive.
diskutil cs list
and take note of the Logical Volume Group ID
diskutil cs createVolume <ID from above> jhfs+ blub 100%
, where blub
is the name you give to the volume.
Link to Apple instructions: Click Here
Note: These are instructions to fix a split fusion drive, but work also for making one.
In the end I went with the most expensive but also the fastest option: #1 which was the Mercury Accelsior PCIe based SSD hardware RAID array (RAID 0 by default which I will keep) in a Mercury Helios Thunderbolt PCIe chassis. The main reason was because it was the only one that mentioned it was bootable (and made a big deal out of that fact).
I paid $799 for the 240 GB model (it's 128 GB X 2 minus the unusable amount...a nice touch for the seller not to count that). It's got a lot of technology built into the card including processors and cache etc. to monitor and control the hardware RAID array including extra error checking and load leveling/balancing. Also it's theoretically upgradable (each drive is called a "blade" and while they don't yet sell independent blades they may in the future). Also the PCIe chassis is an extra bit of the investment that could live beyond the SSD, just like the whole arrangement could live beyond the use of my iMac itself.
This is a great review on it where they say it's "really fast. Ridiculously fast."
A guy on youtube has a (somewhat boring) video of his Mac Pro taking 3 minutes to boot and launch paint shop pro with his hard drive and then after setting up one of these it cut down to 15 seconds! Crazy balls out fast.
This is the sellers sites for;
Of note is that if they didn't offer the bundle discount and if it were not so much more expensive I might have opted for this much more attractive chassis.
Or for even more and larger chassis with multiple slots and supporting larger sized cards.
These chassis got me thinking about the possibilities with thunderbolt. Now any iMac or MacBook can be as capable and expandable as a Mac Pro...there are even developments with video cards in one of these things! I do wonder if it would be possible to take a MacBook Air and hook up a thunderbolt PCIe chassis with a high end graphics card with the display on the internal monitor?
If I was one of these manufacturers, or even Apple, I would consider making a full on chassis with PCIe slots and storage areas, etc. I really wanted a Mac Pro but they were so old...now I can get some of that goodness piecemeal, though for a price. :-)
I get the device about a week from now and will post back my impressions if anyone is interested.
Best Answer
The PCIe flash storage will be faster than the SSD, but how much you'll notice that in the real world is questionable.
The PCIe card used in the new iMacs is the same (custom) stick-like form factor Apple uses in their other products.
You should get the 1TB or 3TB Fusion drive configuration if you want more than 256GB of storage and don't want a larger SSD. You could of course get an external USB3 drive to provide large storage if you prefer, or even get a USB/Thunderbolt external SSD.
The $200 for the fusion drive is expensive, but not insanely so. It will give the most noticeable performance boost of any possible upgrade on the iMac, unless you prefer to spend the money doing an all-SSD setup, which will still be very, very fast.
You're not going to find a compatible PCIe SSD for any less than Apple's upgrade cost. For example, OWC sells compatible SSDs for the MacBook Airs (http://eshop.macsales.com/shop/SSD/OWC/Aura_Pro_Air_2012) that may work, but I don't believe anyone has specifically tested it.
I will also note that opening up the current iMacs is more difficult than in the past, due to the laminating process on the screen to reduce glare, parallax and weight. It would be a false economy to buy a $2000+ computer, only to risk damaging it by opening it up for the chance to save $50. If external storage is not desirable and you want more capacity, go Fusion.