Whether two disks failed at the same time, a resync was carried out the wrong way, or a two-bay box failed with both drives still intact inside it, it doesn't automatically mean that your data has disappeared. Each member of the RAID is imaged separately and we then rebuild your files from whichever copy turns out to be the stronger.
Every RAID is examined by us before we quote. The initial diagnosis costs nothing, and once the examination is complete our written quote starts from £500 + VAT, depending on how many members make up the RAID. If you have a logical rebuild, in most cases you only pay if we recover your data.
A mirror should keep going through the failure of one of its members, but when failures go past this point, the issues described here are the ones that typically end up with us.
Members of a mirror are ordered together and turned on at the same time with the same workload, so whatever wears down the first member to fail also tends to wear down the second, and quite often the second fails only a few days after the first.
A common way for a two-bay NAS or a mirrored external drive to go down is the failure of the bridge board or controller, which leaves two working disks inside a dead enclosure until each one is read on its own.
If you swap the wrong drive (or simply swap the drive as the unit tells you to), the good drive gets overwritten with whatever is on the other drive, which could be blank or out of date. In short, the mirror would end up destroying the very data it was supposed to protect.
When a mirrored pair has run degraded for a while on one drive and then later on the other, each of the two drives will hold a different version of history. If you merge them carelessly they will essentially destroy each other, but if you image each drive separately and keep those images apart, then each version can contribute its own part of the story.
This covers things like a deleted record, a corrupted file, a failed update or a ransomware attack. A mirrored pair is intended to create copies of every write on both drives at the time it occurs, so any damage to one of the drives happens at the same moment on the second drive.
If the firmware in your NAS box fails, or the operating system develops a fault, you may not be able to get at your perfectly working pair of hard drives until they have been imaged and the volume rebuilt elsewhere.
Both disks in this pair are treated as separate cases from the beginning. Each disk is imaged independently on separate imaging equipment (head-swap bench work is done first on any disk that has physically failed), and once both disks have been read, the two images are compared to identify which holds the most complete or up-to-date version of your data. The next step is to build a volume using the image with the stronger read. If there are gaps in it, they may be filled in from the second image, but nothing will ever be written back to the original disks.
The primary function of RAID 1 is redundancy, so you can keep using the volume when a single disk fails. However, other forms of failure go straight through RAID 1 protection, such as deletions and updates with errors, which are copied to both members of the mirror at the same time, ransomware that will encrypt both disks in a single pass, or a failed enclosure that takes out both disks with it. Therefore a broken mirror is a real recovery job, and the overall lesson here is that a true backup sits on separate media in a separate physical location.
We get two-disk systems from Netgear, QNAP and Synology at our lab in Oxford, and from time to time we also receive small office servers, sent to us from places including Swindon, Devizes, Highworth and Malmesbury. Please get a quote first, by phone or with our free online diagnostic, before sending your disks. Both disks can then be sent to the lab together, and the best practice is to label each disk with its bay so they are easily identified and do not get mixed up on the way. It is relatively straightforward to find the lab if you take the A420 from Swindon, and you can hand your disks in at reception Monday to Friday, 9am to 5:30pm, with no appointment needed. If it is not practical for you to bring the disks to the lab yourself, you can put them in a suitable box and send them by next-day tracked and insured post. For further details about the wider service, see RAID recovery and NAS recovery, and refer to the data recovery cost page to view pricing.
We image the pair and rebuild from the better of the two copies. A free diagnostic is carried out first, and then you'll be given a written figure.
Most customers get a quote first, by phone or with the free online diagnostic, and then post or courier their media to us.
Sending a drive from a computer, laptop, MacBook, iMac, CCTV / DVR or server? Please remove the internal hard drive or SSD and send us just the drive (from a server, every disk, each labelled with its bay), as we don't offer a drive-removal service. We don't recover storage soldered to a motherboard (for example T2 and Apple Silicon Macs and some thin laptops), only drives that can be removed and sent to us. If you're not sure which kind you have, ring us first.
↓ Print the booking-in & shipping form (PDF)
Mark the package for the attention of Oxford Data Recovery and we'll ring you as soon as we've diagnosed your media.
Not sure what to send? Ring 0800 689 0668 first or use the free online diagnostic.