So I have a 2012 iMac. I got the base model 21.5" which means I have a painfully slow 5400 RPM hard drive. The pure SSD option would have cost $1,300 ($1 more than the $1,299 base price) if I could even get it but you had to get the 27" to even have the option.

The iMac is very fast with the obvious bottleneck being the 5400 RPM HDD. I want really a better than stock setup with insane speed. Considering that anything under $1,300 is actually a savings (lol) and with the possibility of even being superior in speed to the internal SSD. The issue I'm most concerned with now in my choice is if it will be bootable. This is especially true with the RAID options because as the ones in my price range are SOFTWARE RAID I wonder how it could be possible to be bootable?

I've narrowed down my choices to these four options, in no particular order:

  1. OWC Mercury Helios 240GB Essentially a thunderbolt PCIe expansion chasis with fast PCI based SSD

  2. Pegasus J2 Thunderbolt 2 x 128GB SSDs configured in RAID 0

  3. Pegasus J4 4 drive thunderbolt 2.5" storage chassis, RAID configurable I'll probably get 4 x 64 GB SSDs and configure them in RAID 0 or maybe RAID 10

  4. LaCie Thunderbolt SSD 240GB Kind of the same idea as J2

Any advice would be excellent. Feel free to make an alternative suggestion if you prefer. I'm ready to go as soon as I can make a choice.

Again my machine is:
Apple iMac 21.5", Late 2012 / i5 2.7 GHz / 8 GB RAM / 1 TB HDD / GeForce GT 640M 512MB DDR5 / OS X 10.8

  • 2
    Why don't you just replace the internal HDD with a regular 2.5" SSD of your choice (for less than $200-$300)
    – Alexander
    Commented Feb 12, 2013 at 3:57
  • The third one in RAID 0 is probably going to be the fastest. Assuming each drive can run at about 300 MBps, you got a total performance about 1200 MBps, of course there is loss of performance about 10% max, but that's still 1080MBps, chasing the Thunderbolt limit of 1250MBps.
    – Shane Hsu
    Commented Feb 12, 2013 at 4:16
  • I will suggest you to get drives that runs at about 350 MBps, and 4 of 128 GB drive to achieve the best performance. But no redundancy here.
    – Shane Hsu
    Commented Feb 12, 2013 at 4:17
  • My Mac can boot from an SD card, so I think it should be bootable.
    – Shane Hsu
    Commented Feb 12, 2013 at 4:18
  • @XAleXOwnZX mainly because of the cost, hassle and cringe factor of opening up the micron tolerance tight friction stir welded case but also because the potential of Thunderbolt is for much higher speeds - which is realized in my final choice (I'll post momentarily). Thanks. :-) Commented Feb 15, 2013 at 15:32

1 Answer 1


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.

  • @XAleXOwnZX Would love to know your (or anybody else's) thoughts/comments on my choice? Commented Feb 15, 2013 at 15:55
  • 1
    @ShaneHsu This is what I selected, what do you think? Commented Feb 15, 2013 at 15:56
  • So it's on Thunderbolt and it's bootable. So I think iMac can boot from all external Thunderbilt drive in theory. I actually feel a little bit sorry since I should be able to test this out by putting my MacBook Pro in target disk mode and try to boot...
    – Shane Hsu
    Commented Feb 15, 2013 at 19:25
  • Anyway, I think it's a great setup, PCIe SSDs can be a lot faster than SATA ones, and it offers you flexibility to play with other technologies for the future. I'm thinking Fiber. LOL. I think what I suggested with 4 SATA SSDs won't be much faster than these PCIe SSDs you got.
    – Shane Hsu
    Commented Feb 15, 2013 at 19:30
  • Cool thanks...yah that's interesting what you said about target disk mode. I didn't order my thunderbolt cable as I was going to just pick it up from the Apple store. I think I'll pick it up tonight and try to experiment booting through targeted disk mode...interesting idea. I heard shorter cable has a slight performance advantage? I'm thinking of a 0.5 meters though anyway for a clean setup. Commented Feb 15, 2013 at 22:41

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