OWC Mercury Elite Pro Qx2: Data Recovery

OWC Mercury Elite Pro Qx2
OWC Mercury Elite Pro Qx2

This OWC external enclosure is a common sight on the desks of Mac users with big storage needs. It’s a pretty standard 4-bay box, styled somewhat like a cousin of a PowerMac G5 or 1st generation Mac Pro. Inside are the usual options of RAID 0 to RAID 5 with a few additions like JBOD & RAID 10 thrown in for good measure. There are a few variations of this device but the back panels commonly have USB, Firewire, and eSATA ports for direct connection to a PC or Mac. There is no ethernet port on these drives which makes the Qx2 a DAS (Direct Attached Storage) rather than NAS (Network Attached Storage).

Aside from massive name, the OWC Mercury Elite Pro Qx2 also comes with a potentially huge amount of storage. Currently up to 32TB on the OWC store, but also available diskless or BYOD (Bring your own disks). With so much storage space, these drives often become the one and only repository for vast lumps of important data. The benefits of RAID give a false sense of security that the data is safe from drive failures. Unfortunately, there are a number of reasons why the RAID array alone will not protect from certain failures. Most of  these failures can be overcome by us in our workshop, but they are not one-button fixes. It is helpful to understand why a seemingly rock-solid platform can be even more risky than a simple external USB drive.


Under common settings, the Qx2 will use RAID 5 for the array. With four 2TB drives this gives you a 6TB volume on a Mac or ~5.5TB on a PC[1], and can cope with a single disk failure. There is a lot of debate about how good RAID 5 really is for such large drives[2]. In our example this means that if a single disk fails, it will need to be replaced, and then the new disk rebuilt with 2TB of data calculated from the other disks. This will take many hours, even under optimal conditions, but if anything goes wrong before it completes the array could stop showing up all together. At this stage, the data is probably recoverable but don’t panic. One wrong move and the data could be gone for good.

If the data is crucial then get assistance from a RAID recovery service now and you should get back all or most of the data.

If any disks are removed or replaced at this point the array could get reinitialised and either make the recovery more complicated or wipe the data completely.

Other Failures

Aside from all the problems with a RAID setup, the volume could also fail in the same ways that a standard hard drive can. There could be deleted files, a reformatted or corrupt partition, or even the RAID controller failure. RAID cannot protect against those types of failure at all.


Our first step would be making read-only copies of each disk in the array. This protects against further disks failing, and also allows us to work from copies without risking the original disks. In fact, once the disks are copied, we put the originals to one side and don’t touch them again until all the data is recovered and supplied back to the user.

Once we have our copies, they are loaded into our own hardware where we recreate the RAID in a virtual environment. Again, we don’t use the original hardware, as that may have been the root cause of the problem.

When the virtual RAID has been loaded and all the data extracted, the files are supplied back on whatever alternative storage is suitable, (not the original device!) Once the data has been delivered to the user, and backups made, the old unit can then be destroyed, or returned and reused.


Anyone using RAID on a regular basis should know that RAID is not a replacement for backups. If anything, the increased number of disks makes failure more likely. This needs to be addressed by either making backups to another device, or an online service (preferably both). You ideally want backups that keep historic versions of the files, so that inadvertently deleting a file or changing a file by mistake will not also replace the backup version.

If you are having problems with an OWC Mercury Elite Pro Qx2, give us a call or send a message via the form on this page. We give free advice and could help you avoid permanent data loss.

1. Macs now use 1000 bytes for 1KB but PCs use 1024 bytes.

2. Even RAID 6 does not solve the long time required to rebuild a disk, even though it allows for two disk failures.

4 Replies to “OWC Mercury Elite Pro Qx2: Data Recovery”

  1. Hi. I am experiencing the same problem as Bernhard. Actually it has happened before, I mean, one day the enclosure starts rebuilding and it would take forever… but the first time it happened I’ve just took out one of the disks and put it back in, and it became OK again. But now it won’t finish rebuilding after more than 48h. And I am afraid that turning it off while rebuilding (for more than 48h… would that be normal?) may have made things worse. I am using 4 x 3Tb disks, in RAID 5. Problem is don’t have other disks I could copy these to. Woukd you have any suggestion other than that? Thanks

    1. Hi Pedro. It sounds like you’ve got a bad disk in there. You can’t always trust the LEDs for diagnostics. I would never carry out a rebuild on a live RAID array unless I had a backup of it first. Rebuilding causes the parity to be recalculated, so if it goes wrong, you’ve lost some of the recovery options. Without usable parity information, you need all four disks to be accessible for the recovery. If you can’t send it off for pro recovery then I would suggest cloning all of the disks, and then recovering the data from the clones.

  2. I am running my Qx2 with four 2GB Hitachi drives using a RAID5 with parity configuration. It’s been running fine since 2012, but yesterday it did not come up after I turned it off and on again. When starting up all HDD LEDs are blinking, then the device switches to the yellow blinking ‘rebuild’. It did that for more then 24h. If a HDD has a failure there should be a red LED for the HDD, but there isn’t.

    I am wondering if the drives are fine, but the Qx2 unit is defective and if I should get a new one to recover the data.

    1. Hi Bernhard. We have seen similar types of failure with these devices. The problem could be a combination of the external enclosure and also the disk contents. Moving the disks to a new enclosure could cause a total rebuild, which would destroy the existing data. Also if the problem is on-disk then moving to a new enclosure won’t help. It is also a concern that a 24+ hour rebuild has happened. Hopefully That didn’t cause an even bigger problem but it may have changed the disks. There are so many variables with this type of array that I wouldn’t suggest you try anything more without first making full disk copies.

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