One of the reasons I like Macs is that their useful life tends to be significantly longer than that of a typical Windows machine. This is especially true of the pre-Retina MacBook Pro models, where it’s trivial to upgrade both the RAM and the drive.

I’d previously swapped out the 750GB hard drive and optical drive that came with my late-2011 MacBook Pro 17 for two 1TB hard drives. Along with a RAM upgrade, that gave me a 16GB RAM, 2TB hard drive machine. The plan was to use the machine in that form for a year or two, then do a further upgrade to SSDs once 1TB models arrived and fell to a halfway sensible price.

When that finally happened, and I did the upgrade, that gave me two 1TB hard drives surplus to requirements. I could have placed each into its own external drive caddy, but one 2TB drive is more useful than two 1TB ones, so I decided instead to try out OWC’s Mercury Elite Pro mini. This is an external enclosure for two 2.5-inch drives, which supports both USB 3 and Firewire 800, drawing power from either source – making it a portable drive without the need for external power … 

Installing drives into the enclosure is trivial even for non-technical types, thanks to the extremely comprehensive instruction booklet with clear, step-by-step photos. If you can use a screwdriver, your skill-set is complete.


Undoing two Philips screws on the backplate allows you to slide out the innards.


Inside, OWC supplies the eight Philips screws you need to secure the two drives in the caddy. Remove these, and the silica gel packet, and you can then slot in the two drives. Simply place each one loose in the caddy, line up the SATA connection with the slots and push firmly into place.


You do have to press down a little more firmly on the right-hand drive, which sits on top of a clip holding two cables, but it’s a simple, 10-second job.

Once the drives are in place, flip the unit upside-down and insert the four screws which attach each drive.


The instructions suggest you hold the unit in your hand to press the drives flat against the bottom-plate while doing this, which is easy to do.

Once secured, you need to set three DIP switches to tell the unit which mode you want. There’s a choice of RAID 0, RAID 1 and Span. I chose RAID 0. This makes both drives look to OS X like a single drive, with data spread across the two. It does, though, mean that a failure of either drive will result in loss of data. This isn’t a great concern to me, as it will be used as a media drive, so everything on it could be re-downloaded if needed.

If you want internal backup, RAID 1 gives you the full capacity of one of the drives, and mirrors all the data to the second one. Finally, if you are using two drives with different capacities, Span mode acts like RAID 0 in that it makes it appear to OS X as a single drive, writing data to one until that drive is full and then writing further data to the second one.

That done, slide the caddy back into the enclosure and re-attach the back-plate using the two screws you removed earlier.


That’s it: no cables to attach, only a total of ten screws. Connect to USB (newer Macs with USB 3 ports) or Firewire (older Macs), slide the power switch on and you’re up-and-running. Both cables are supplied, and both power the drive from the port.

With the job complete, you have a stylish-looking drive that matches the quality of any ready-made drive out there and is an excellent match for a Mac.


There are two Firewire 800 ports, so you can daisy-chain them if desired, though you will need external power to do that. OWC offers an optional power supply for this use.


In use, two blue LEDs light up to confirm both drives are operating.


With RAID 0, I was seeing both read and write speeds in the 60-70MB/s range on Firewire, which is on a par with what I’d expect from a single external drive.

At $89.99, it’s not the cheapest solution out there, but I do think it’s a decent value for what you get. It’s a very stylish design, very solid build – and the built-in RAID gives you the convenience of combining the capacity of two drives into one. It’s available direct from OWC, with free shipping.

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28 Responses to “Review: OWC Mercury Elite Pro Mini dual-drive external enclosure with RAID”

  1. Joseph Moore says:

    What kind of performance did you get out of Raid 0?


  2. Thanks for the review. Although it is a bit shallow, as you don’t say anything about the drive’s performance.

    I own it myself and am quite happy with it. I didn’t do any speed tests, but I would think it is on par with a singke 3.5″ drive… or maybe a tad faster. It is fast enough for me to serve as a 10.10 test system.

    Pricey… yes. And TB would have been nice, too… but overall I can still recommend it. Plus there’s not soooo many 2.5″ multi-bay solutions out there anyways…


  3. SInce you’ve made specific mention of non-technical users (if you can use a screwdriver your skill set is complete), I think it’s important to note that RAID 0 substantially increases your risk of data loss, since a failure of either drive means the loss of the data on the volume. The point of RAID 0 is speed, not data integrity.


  4. So true about apple being more upgradeable and lasting longer. I don’t know any windows based laptops where you can do this.

    I have a 2011 Sony I have upgraded a couple of times as ram prices came down and hard drive capacity went up. I am going to call that this one is a little bit biased Ben.

    I would have liked more of a mention on the build quality, in the pictures the edges look a little sharp. Are they slightly rounded on the front and back edges? If not I have had some bad experiences with edges like that and cables in a bag before.


  5. Why there’s no thunderbolt? Wouldn’t it make sense for older iMac users to attach two RAID SSDs instead of trying to remove that huge LCD panel?


  6. Joel Senders says:

    You should test your speeds while having only one single drive in the enclosure and compare to your RAID 0. I am willing to bet they are comparable. Likely the reason why you are getting 60-70 MB/s speeds is because FireWire 800 has a peak transfer rate of 100 MB/s and a typical sustained throughput of around 70-80 MB/s. Thus you have a bottleneck. Since you have a late-2011 17″ Pro, there is no USB 3.0 and you only have two options for getting around it: 1) use a Thunderbolt enclosure or 2) buy an Expresscard/34 USB 3.0 card.


    • Ben Lovejoy says:

      In real-life, Firewire 800 is faster than USB 3, giving lower peak speeds but higher average ones. The speeds I’m seeing are in line with what I’ve seen in external single-drive units.


      • Joel Senders says:

        You mean FireWire 800 is faster than USB 2. FireWire 800 is not even close to as fast as USB 3.


      • Ben Lovejoy says:

        Sorry, yes, was comparing with USB 2. USB 3 in theory is faster than Thunderbolt though not tried a back-to-back comparison myself.


      • Joel Senders says:

        Hm. Not sure where you are getting that from. The bus speed is almost unilaterally inhibited by the drive it is using (which was my original point). Thus, if you have a drive that peaks at 10 MB/s read/write, FireWire 400/800, USB 2/3, Thunderbolt, etc. are all going to have very similar speeds in accordance with the peak rate of the drive; the drives ability to spin and put data on the bus is the limiting factor. So in that case the interface/bus type hardly matters. And that is true of most external hard drives; the bus speeds now are so high and the bandwidth is so large that you will never saturate the line. It’s like having a large water pipe and only pouring a small amount of water down it, and then, when you want more water coming out the other side, you increase the pipe size instead of pouring more water down. That is why USB 3.0 and Thunderbolt are so close in comparison, because they are both usually compared with data rates that fall within both of their ranges (625 MB/s and less). However you will see the superiority of Thunderbolt over USB 3.0 when you break that threshold (e.g. multiple SSDs in RAID 0, server storage applications, etc).


      • Ben Lovejoy says:

        Right – what I’m saying is that the external drive enclosures I’ve used are all giving similar speeds, so I don’t think RAID 0 is a factor here.


  7. ricardogomez297167426 says:

    Curious: Is the USB cable the type that have two connectors on the end to add power to the enclosure?

    I can see the appeal of a drive like this. Especially us photographer/video types. But more about redundancy than capacity. Small and no power adapter. You’d spend about $40 for two enclosures, but you’d add cables as well. And you’d have to have two, individual copy processes to accomplish the same thing. Having one drive and one cable is definitely a convenience worthy of the price difference.


  8. telecastle says:

    Ben, did you have to load any drivers so that the OS would recognize RAID? Is my understanding correct that this enclosure has hardware drive, and that regardless of what RAID level you configure with DIP switches on the enclosure, the OS will see this enclosure as one drive?


  9. On the a slightly different focus… I was wondering what brand did you get for your 16 GB RAMs?
    I have been using Corsair compatible ones on my 15″ mbp early 2011 and it has been a nightmare with the kernal panics.