OWC’s New Qx2 Brings RAID 5 to the Home Desktop

| In-Depth Review

The OWC Mercury Elite-AL Pro Qx2 is a consumer-grade RAID storage system that can support RAID levels 0,1,5 and 10. It's a modest sized, handsome aluminum enclosure that has slots for four user-replaceable drives. It's one of the first consumer RAID 5 or better systems, and the benefit is that a failed drive can be hot swapped out, the data rebuilt from the parity drive, and result in no loss of data. And it's fast, quiet and nicely priced.

Some Background - Why You Need RAID 5

We're all familiar with RAID level 0 and 1, even though we may not be familiar with that technical term. Basically, RAID level 0 is striping. Data is split between two drives so that the system can accept data at a faster rate. The downside is that if one drive fails, all data is lost.

We're also familiar with mirroring. That's RAID level 1. Two matched drives are used, an all data is written to both at roughly the same time. It's no faster than a single drive, but if one drive fails, there is a duplicate data on the other.

Previously, RAID 5 systems have been expensive and reserved for enterprise use. In RAID 5, data is striped but parity data is distributed across all the disks and there's a dedicated parity drive. As a result, because of the way the data is distributed, the system can tolerate the loss of any one drive. Simply replace the defective drive and the system controller rebuilds the data set. RAID 5 is popular because it's an inexpensive way to obtain complete redundancy.

RAID 10 (or 1+0) offers redundancy in a different way. Data is striped over two mirrored pairs (in the Qx2). Again, if any one drive fails, no data is lost. A drive replacement and rebuild is all that's required. While faster than RAID 5, the capacity, compared to RAID 5, is reduced.

The OWC Mercury Elite-AL Pro Qx2

The Other World Computing Qx2 is basically an enclosure that contains the power supply, electronics, RAID controller, four SATA slots and cooling fan. One can purchase the system with from 500 GB to 2 TB drives. My review unit had four 500 GB drives for a formatted RAID 5 capacity (my choice) of 1.33 TB. (The redundancy algorithm chews up that other 0.67 TB).


Qx2 size

Qx2 size comparison

The photo above shows the relative size of the unit compared to, left to right, a LaCie Big Disk (1 TB) and a NewerTech Guardian MAXimus RAID 1. Specifically, it's 9.5 x 5 x 7 inches. (24 x 13 x 18 cm.) and weighs just under 9 lbs (3.5 kg) empty. It's likely bigger than any hard disk you have, but neither will it chew up monstrous desk space.

Qx2 inside

Inside front cover

Set Up

OWC has made the set up as simple as humanly possible. You set the enclosure on the desk, open the front cover plate with one of the two keys included, slide the four drives in and seat them, turn the thumbscrews to secure the drives. Then select one of the RAID settings according to the instructions with the circular RAID Selector Switch on the upper right, then close the front door. Then connect the chosen interface, FireWire 400/800, USB 2 or eSATA, connect the power cord, then turn it on. It's that simple.

Qx2 OWC Promo

Front (cover removed) and back

The system comes pre-configured as RAID 5 and HFS+, which is the expected use. I asked about the USB 2 port because, compared to FireWire 800 and eSATA speeds, USB 2 is fairly slow compared to the ability of FireWire 800 to sustain 80 megabytes per second (MBps) transfer rates. OWC said that it was added merely for the sake of being more universal in its connectivity. I wouldn't dream of using it that way.

The first time I booted it up, it appeared on my desktop as if it were a 1.33 TB conventional drive. It runs as quiet as any of my other drives which is pretty good, considering that it has four drives and a large fan. (The fan uses ball bearings, not sleeve bearings, which is a Good Thing.) The drives run at 7,200 RPM.


I am not a professional hard disk performance tester. However, I am familiar with some of the tools available. For example, QuickBench 4 provides data on random read & write vs. sequential read & writes for a given block size. I used it to provide a rough estimate of the performance, using FireWire 800. Here are the results, showing 85 Mbps sequential read.

Qx2 perf-1

Performance, unstressed

I also conducted some long term stress testing of the unit by re-doing the QuickBench test with four high definition, 1080p, movie trailers, from Apple, running in a loop for 30 minutes. (This is similar to a test I did last week, but for a longer duration.) I did this to see if the unit warmed to the touch or whether the exhaust fan air seemed to heat up. That didn't happen, it appears, because four 1080p trailers hardly stresses the total system -- and the Qx2 was still able to simultaneously crank out 68 MBps in sequential reads.


Qx2 Perf-2

HD Stress test plus QuickBench run.

The conclusion I drew from this test is that, in normal operation, casual home users are unlikely to over heat or over stress the unit.

Construction Quality

The aluminum enclosure, the thumbscrews to secure the drives, the size and low noise of the fan, the large rubber feet were all deemed first class. The lockable cover-plate, which also serves as a (barely sufficient) air filter, secures the drives from tampering by other members of the household -- the youngest of whom may have a fetish for turning knobs.

The fan takes up a considerable amount of area on the back of the unit, and that's good because a big, slow fan is quieter than a small, fast rotating fan. I thought the overall quality of the unit was amazing, and I'd be happy to own one of these units.


For enterprise use, one might expect considerable documentation. However, Mac users are more inclined to understand the rudiments, then they just want to get going. Basically, the 11 page manual guides the user from out of the box to some basic RAID terminology, then how to assemble the unit (inserting and securing the four drives), a brief FAQ, setting the RAID mode, and finally support information.

A series of colored LEDs on the front not only provide status information, but also confirm the RAID setting. For example if you select RAID 5, the "big" plus "fast" lights glow. There is also a rebuild indicator so that you know the unit isn't available while it rebuilds data after a drive replacement. (Rebuild time depends on the total storage, and I didn't test that part.)

One thing the manual doesn't explicitly cover is that system allows for hot swapping, just like the more advanced, enterprise-class systems do: the old Apple Xserve/RAID and its successor, the Active Storage XRAID. No need to shut the unit down to replace a failed drive.

Also included is a CD that includes OWC's shareware, Prosoft Engineering Data Backup for Mac, NovaStor NovaBACKUP for Windows, and Intech SpeedTools for Mac. The QuickBench 4 test I conducted is part of that suite.

Associated Technical and Support Issues

RAID 5 systems got their first use in the enterprise. Bringing that technology to the home user's desktop presents several issues: support and technical management of massive RAID 5 storage. To that end, I drew upon my on experience with the Apple Xserve/RAID, now discontinued, to ask OWC some technical questions. They quickly responded via e-mail.

1Q. How far can the unit be expanded?

1A: The Qx2 is currently limited to 4 x 2 TB drives. The operating system must be able to support 8 GB volumes. (Mac OS X Leopard does.)

2Q: The fan pulls air from the front of the unit to the back. Could the thumbscrews produce shavings that could be drawn into the drives?

2A: Minute chance of that. We have not observed any metal shavings being created, most likely because the threads are die tapped treaded for multiple screw install/removal sequences.

3Q: What is the maximum operating temperature? Sometimes, it gets up to 80F in my office in the summer.

3A: No problem. Operating temperature is 5°C to 55°C (41°F to 131°F)

4Q: Is there any form of vibration isolation to inhibit acoustic coupling between the four drives?

4A: No, but when possible for each size Qx2 (but always for the enterprise versions), we make an effort to use drives that have technology to reduce those soft errors that happen from cross-drive vibrations.

5Q: Does the RAID controller attempt to manage the drive heads in such a way as to minimize violent travel of the read/write heads?

5A: No.

6Q: Does the cooling fan use a sleeve bearing or the more superior ball bearing?

6A: Ball bearings.

7Q: What is the rating of the hard disks supplied, not MTBF, but the class of drive?

7A: We offer Enterprise-class units that have a 5 year warranty.

8Q: If the fan dies, does the unit self-detect and shut down?

8A: No.

9Q: Are the fan and power supply user replaceable?

9A: No.

10Q: Enterprise RAID systems use a cache for high throughput. Is that true for yours?  The old Apple Xserve/RAID had a battery backup system so that in the event of a power outage, the cache could be saved to disk and data integrity maintained.  Tell me what happens to the Qx2 and cache coherence if power is abruptly cut.

10A: Incorporating this would have added extra costs that would have brought us away from the price range we were shooting to be in.

11Q: Does OWC offer a service contract for on-site repair?

11A: Not currently, but it's been discussed internally.

12Q: RAID 5 offers an additional level of redundancy, but it could happen that a proper analysis of a failure could require the user to return both the chassis and the drives for evaluation. What is OWC's policy regarding the disposition of user data?

12A: We have multi-bay RAID specialists that will work with you to determine what the best course of action is. Since there are elements outside of our control, we can’t guarantee the data, but every effort will be made to save the data ( using level 1 data recovery techniques)  and transfer it to a new drive or drives if that is where the problem is.

No packages are opened outside of the return room which is a secure area with very limited access. If we determine a drive needs to go back to the manufacturer, we perform the following before it is sent out to protect your privacy:

  • We "wipe the drives", when possible, by initializing the units.
  • For drives we (OWC) dispose of, the platters are physically destroyed by hammer blows prior to disposal.
  • For units that are manufacturer (warranty) returns that are inoperable, we are unable to wipe directory or data.

13Q: Is the RAID controller a custom design?  Or is it derived from a RAID controller built for other enterprise class RAID systems?

13A: The Qx2 is utilizing the Oxford 936QSE Controller.

I asked how much it would cost to replace a key (two supplied), but OWC hasn't defined a price or policy on that.

Home, Small Business IT Planning

All storage technology demands some awareness of technical issues. Manufacturers try to make their products simple to use, and in this case, OWC has succeeded. But ease of use doesn't imply that we don't need to plan or that we'll be carefree forever. So while the the OWC Qx2 is a very nice device, the user still has to think about a few things. I bring this up simply out of due diligence.

  • If a cheap terabyte drive, used as Time Machine backup fails out of warranty, one might elect to destroy it, buy a new one, and re-create the backup. (Losing archival data, of course, from the original epoch.) With the Qx2, options are more complicated due to its cost.
  • If a single drive fails, how long can one afford to be off the air while a replacement arrives? (Unless one uses the Spare Drive mode -- which reduces the over all capacity to two drives out of four.) An external, standby, spare is a good investment considering how cheap storage is.
  • If the source of a problem is indeterminate and the unit needs to be returned with the all drives, is one prepared to have several terabytes possibly in the hands of the drive manufacturer for warranty replacement? Or if the Qx2 hardware checks out, is it better to simply order the defective drive destroyed, swap in a new drive and pay for it -- even if under warranty? Also, shipping a loaded Qx2 is neither cheap nor convenient for the home user.

Some of these questions can't be answered until consultation with OWC warranty repair. But the bottom line is that while RAID 5 and 10 redundancy is nice to have in the case of an obviously failed single drive, such a system doesn't immunize the home or small business user against all possible problems.

In the enterprise world, matters are more straightforward -- for a price. A field technician, under service contract, conducts hardware diagnostics on an enterprise class system at the customer's location. Components or drives can be swapped out. If only a drive is defective, a new one is installed, and the bad one is given to the customer for disposal, destruction, etc.

OWC Promo Qx2


The OWC Mercury Elite-Al Pro Qx2 comes with a three year warranty, if you buy drives from OWC, and enterprise drives have a five year warranty. The unit is well manufactured with excellent fit and finish. Most users will be able to put it together and be up and running from box to desktop icon in 20 minutes or so. The documentation avoids complications and provides the essentials, in a kind of Macintosh Way. Drives are hot swappable, and the cooling system seems robust.

A sustained sequential read speed of at least 80 MBps (640 Mbps), with FireWire 800, was tested and confirmed. Cables for all interfaces are, in OWC's tradition, included.

However, some compromises in design had to be made in order for OWC to hit the desired consumer price point. The drive should be connected to an UPS because it doesn't have battery powered cache. It'll be up to the user, with the unit on a desktop, to monitor its health. There are no remote diagnostics, alarms, and e-mail calls for help like the higher level enterprise system that sits unattended in a data center. Given the compromises made and the price point hit, I can absolutely recommend this product for the slightly more advanced home user or small business.

Sample Pricing

  • Empty enclosure: US$379.99
  • 4 x 500 GB: US$579.99 (consumer)
  • 4 x 1 TB: US$799.99 (consumer)
  • 4 x 1 TB: US$979.99 (enterprise)
  • 4 x 2 TB: US$1,599.99 (consumer)

See OWC's complete pricing page.

Product: Mercury Elite-Al Pro Qx2

Company: Other World Computing

List Price: See text



Brings RAID 5 technology to home, small business, high quality hardware, plenty of indicator lights, hot swappable drives, FireWire 400/800, USB 2, and eSATA ports, cables included, nicely priced, backup software included, 5 year warranty on Enterprise-class drives.


Limited to home and small business due to a few technical limitations. No air filter. No user replaceable parts except for drives.

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I would prefer to see an Ethernet connection. My NAS sits on the network so that all of our computers can access the data. With this product I can only connect it to my Airport via USB - a poor way (as you noted) to connect the drive.


I am looking for a NAS also. I have been looking at HP EX485 MediaSmart Home Server.  I wish Apple made a home server.

John Klos

Here are a few nits to pick: RAID-0 is not RAID, because there’s no “R” (redundancy) in striping, but everyone makes that mistake. Also, it’s striping, not stripping. Stripping is what some guys pay $$$ to go see.

Second, you got 1.33 TB of formatted storage because 1 TB of drive space is not equal to 1 TB of actual space (1073741824 != 1000000000). RAID-5 reduces the amount of usable space by the equivalent of one drive in the set, so that’d be three out of four 500 gig drives, or 1.5 TB (1500000000) out of 2TB (2000000000). 0.67 TB would be a pretty arbitrary amount of space in a RAID set with 500 gig drives.

I’d like to add two other points: one, drives don’t normally get any hotter with heavy usage. If they’re spinning, they’re generating most of the heat they’d ever generate. Another point is that when you’ve got some sort of RAID setup, there’d almost never be a reason to not run them on a UPS, even if they don’t have a battery backed cache controller. Regardless of that, though, using HFS+ with journaling is good protection from that.

I’ll be looking forward to trying one of these myself. Thanks!

John Martellaro

It’s clear that stress tests that used to bring a Power Mac to its knees are a piece of cake for a Mac Pro, FireWire 800, and this Qx2.  As for striping, it’s keyboard bounce I tell you. Yes, that’s it.



Thanks for the review, I was looking for this for some time! Any info on the write speeds this drive can handle?

On question 10: does this mean this enclosure has no cache at all?


John Martellaro


Of course, the drives themselves have their usual cache. 

Sequential write speeds were on the first chart, the red line. Peaked at 66 MBps.


Let me tell you, I’ve had quite the run with this product, and I have to say, I am not happy.

Currently, I’m on my 3rd unit. The first unit they sent (ordered about an hour after they were originally announced as available, well before this price reduction) I am pretty sure was a test mule, as the packaging was different, and the unit came assembled, but with a different RAID configuration out of the box than was stated in the manual.

Within 2 days, the array started going offline randomly, and wouldn’t go back online (it wasn’t seen by Disk Utility), and the only way to bring it back up was to cycle the power. Then the rebuild light went “solid on”, which isn’t supposed to happen, and one of the drive lights went on (indicating a failed drive). I was asked to move the drive position, to see if the failure light moved with it? it didn’t, which would indicate something else was wrong. So I sent that entire unit (drives and enclosure back).

Their customer service was eager and pleasant, however, they would drop the ball without contacting me for days.

My second unit arrived (Cross shipped), in new, sealed packaging, with the enclosure and drives separate (home assembly required, and everything totally sealed). I noticed that the RAID level was as it was supposed to be (set to RAID5). I plugged it in, gave it a test run, and copied my data to it. I was a little paranoid. Everything was fine the first 24 hours. Then, out of nowhere, the alarm would go off (boy is that loud at 3am!). However, the rebuild light wasn’t on, nor was there a disk fault light. The array was still mounted, so I unmunted it, and cycled the power. The alarm didn’t go back on??for another 18 hours. Still, no fault light. This time I merely squelched the alarm (the little black button on the front of the case behind the bezel).

Weeks went by, and all was silent (I don’t turn off this machine), until Friday (10 July), when I noticed the array wasn’t mounted, and the rebuild light was stuck on, but no disk fault light was on. I cycled power, but no dice. I tried other connections (FW800, 400, USB), and other computers (G5 tower, macbook), but still no resurrection. I kept the device powered up for over 48 hours, in hopes that whatever it was doing would somehow fix itself. It didn’t, so I contacted OWC, and now I am on my 3rd unit.

They X-shipped a new enclosure (received today 14th July) (kept my disks), and I put the old drives into the new enclosure??I still have the solid rebuild light, and no disk fault. I put my ear to the enclosure, and I don’t hear any writing nor seeking, although I do hear the drives spinning.

I’m now of the belief these problems are endemic to the product, and not “just me”, and I am pretty upset about all of it.

Oh, and while I had them on the phone, I asked about RAID-level migration (the ability to expand a RAID pool by replacing the drives one at a time with larger capacity drives), and this unit, unlike my internal RAID5, *DOES NOT SUPPORT THIS FEATURE*, which makes it less useful to me. It also doesn’t support any feedback of any kind, so you don’t have any idea where it is in the rebuild process, or SMART status of the individual drives. If you care about your data, look elsewhere.

Dave B.

I have a Seagate Black Armor 420 which I added a 3rd drive. It’s a NAS server with two Gigabit Ethernet ports and 4 USB access points one being on the front panel.  So far so good and it’s very quite.  It’s a bit Quarky to set up but once it’s set it seems just fine.  I use it as my itunes server.. However I keep the mail Lib on the tower and sync it to the NAS when I get new songs or movies.

Dave B.

I forgot It’s set for RAID 5


I?m now of the belief these problems are endemic to the product, and not ?just me?, and I am pretty upset about all of it.

Your experience with the Qx2 is pretty much identical to mine.  As far as the rebuild light and drive failure lights, mine were flashing, not solid.  Every product I’ve ever purchased from OWC has worked great, until this one.  I sent it back once and they replaced the board.  It worked awesome for a week or two, then the rebuild light started flashing again and 24-48 hours later the drive dropped off the map completely.  When I reboot the computer it tells me that the disk I plugged in is unreadable and tells me to initialize, ignore, or eject.  I ignored, hoping that I can recover my data.  In disk utility, the volume I created is gone and disk4s2 shows up instead.  It’s like the unit randomly wiped everything on its own.  I got this because I wanted something that I could use for video editing that would be relatively inexpensive, fast (with eSata), and safe (RAID 5).  Turns out it wasn’t as safe as I thought.  Now I’m kind of screwed because having this thing kaput is keeping my from doing my work and I’m losing money.  Octothorpe, have you found another solution?  Someone at the Apple Store told me about these: http://www.granitedigital.com/sataproducts.aspx


It’s more expensive, but I’ve used their products in the past, and they’re geared specifically for video editing:


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