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NDR / Devices and media / RAID 1 mirrored pairs

Specialist · two-disk mirror sets

RAID 1 data recovery for Nottingham. Send the pair: half of what comes home sits on the disk that never failed.

The initial price for the service starts from £500 + VAT for RAID, NAS and server work. There is no charge for the diagnosis that works out how much it will cost. Each block written to the disk is duplicated (mirrored) to the second disk, so theoretically you would have all of your data available to rebuild your volume if either disk were to fail. However, in practice what we see here are the cases that theory does not allow for: two disks wearing down at the same time because they came out of the same carton, a worn RAID controller applying identical corruption to both sides, a re-sync where the failing member is copied over the good member, or a box that lost one of its members in the spring and has run off one disk ever since. Each individual disk is cloned, read-only, and the clones are then compared block by block. The volume is built from whatever blocks each side can still prove it holds; anywhere the two disagree, the newest version is used. Sets arrive by post from Nottingham, Beeston, Ilkeston, Chesterfield and Melton Mowbray, and your own disks come back unwritten to.

Only pay if we recover your data, on most jobs Free diagnosis first, then a single price, in writing Parcels come in from Derby, Lincoln and Loughborough

Ask an engineer and the first look is free
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What a RAID 1 mirror's symptom points to.

Not yours? Open the fault finder →
What is happeningWhat usually causes itWhat that means for you
The NAS says the volume is degradedOne member has gone. Whatever is now left in the bay carries the volume with no disk behind itCopy what you can, then post the pair
Both disks are slowing down, and both were put in on the same dayMirrored members log identical hours, so they wear at much the same rateTake the power off the box now
A new disk was installed and the readable side was emptiedRe-synced the wrong way round: the failing member was written over the sound oneStop there, and post the pair
The same files are absent from both membersWrites go to both sides at once, bad ones includedDo not allow a re-sync
Nobody noticed the amber light until this weekThe mirror has run on a single disk since then, with nothing behind itPost both, not only the dead one
Windows reports the mirror as Failed RedundancyThe set has lost a member. Both disks are often perfectly soundDo not reactivate it and do not import it
How to pack and post it: get a quote first. Movement kills a damaged drive, so you need to pack it rigidly. Insure the package for what the files are worth, not how much the disk cost. Then put a tracked label on the package for the intake lab. We pay for the return postage. If you like, ring before sealing your package so that we can check your packing is adequate. The whole process is outlined in our packing and postage guide.

A mirror covers one thing. Here is everything it does not.

Two-bay NAS units mirroringThis could be a Synology, a QNAP or simply a two-bay enclosure, with the safer of the two options selected when it was set up. Since this uses Linux software RAID, the description of the mirror lives on the disks and not on the enclosure. So your box can stay on your desk, or come in whole if the disks won't come out of it.
Mirrored boot pairs and controllersThe pair a small server boots from, mirrored using either a hardware card or Intel RST built directly into the motherboard. Regardless of how it's paired, a record of the set is written to both disks. That record can be pulled out of the clones without needing the hardware card or the machine it sits in.
Mirrors in Windows, mdadm and ZFSStorage Spaces or a mirrored dynamic volume under Windows, an mdadm pair under Linux, or a simple ZFS or btrfs mirror within a NAS. Each of these writes its configuration to each of its members, each can be built up on clones, and each has its own method of deciding which member to trust (which is exactly the question once they fail).
Why a rebuild can make things worseParity sets let a rebuild work out the missing disk. Mirrors have nothing to work out, because one member is simply copied over the other, whichever way the card has decided. If it makes the wrong choice, you lose your good copy by teatime. All of the work here is done on clones, so an incorrect choice can cost an afternoon, but no more than that.

From the parcel arriving to the files going home.

01

Booked in the day it arrives, and the first look is on us Free

Your case number is assigned when the item is received. Then an engineer works out what went wrong (no charge). At this point, you receive a basic summary of which parts are recoverable and which are not. You also receive a single written quote for the price of the recovery. Accept the quoted price or turn it down, and there is no obligation to pay anything.

The first look is freeOne fixed figure, in writingNo charge at this point
02

Each disk cloned by itself

Each disk is duplicated end to end behind a write blocker. No files will be opened until duplication has been completed. All drives get the same amount of time regardless of whether they failed, because on a mirror set each disk holds half of what comes home. The weakest areas are worked in short passes, last. No byte goes back on the disks you posted.

Nothing goes back onto your disksEach member on its own
03

The two clones set against each other

Where the two sides do not match, the person doing the work has to decide which one to trust. Each member records when it was last written, and the file systems on the clones fill in what the metadata cannot; preference goes to the side that reads and to the newer side. The reasons for each choice are documented for you instead of you having to take them on faith.

The newer of the two establishedSet side by side, never assumed
04

The volume rebuilt over the clones

After this decision has been made, the volume is layered over the clones and the file system repaired there, without touching your original disks. Your files are then opened (ledgers, shared drives, databases, photographs) instead of just being listed, because a name in a list does not necessarily mean anything. Anything that comes back damaged will be reported as damaged.

Every file opened, not countedDamaged files listed as damaged
05

The file list comes before the bill

A complete file list will be provided before any invoicing. Simply say "yes" or "no" to what we found: yes means it is billed, no means it is not, and in most cases you only pay if we recover your data. What we find is posted to you on media purchased specifically for your case, at no additional cost to you. We consider the process complete once you have opened those files yourself on your own computer.

Nothing is charged until you agree the figureNew media, bought in for your jobWe pay to send it home

What comes in most often

  • No one has ever sold you a mirror as a backup: every time something is written, both disks receive that write at the same moment. So a deletion, a bad write or a ransomware attack is reproduced faithfully on both sides. The only thing protected against is one disk failing. Worth having, and that is all of it.
  • Disks bought together tend to fail together: one batch, one shelf, one cabinet, one set of operating hours. In many cases, when the first member fails, the second follows within a few weeks, so the extra time a degraded mirror gives you is much less than most owners realise. The surviving disk in the bay is not always the healthier disk, either.
  • The direction a re-sync takes decides everything: one disk is written across the other, and the card picks the direction on its own internal logic. Just about every bad job that ends up on this bench started with a good side being overwritten by a failing side, or a newer side by an older one. If a box offers to rebuild, refuse it and call us before doing anything else.
  • Post us the disk the box condemned: often that is the disk with the newer data, and often it reads well enough to be worth cloning. Hold on to it and you may lose half of what could have been done before we begin; sometimes you lose everything.

The honest limitations: storage is all this bench does. Mirrors are this page's subject: a pair inside a network box, a pair in a desktop enclosure, a pair on a hardware card, a pair using Intel RST, a mirrored Windows volume, an mdadm or ZFS pair, arriving degraded, written over or re-synced in the wrong direction. Read both sides, and the volume is rebuilt above the clones with your folders back as you kept them. Blocks that have gone on both members cannot be conjured by anyone: certain files come home with holes in them, and those files are named for you in the report. Overwritten data cannot come back either. Encryption needs its key from you. Phones and tablets are not taken. Prices start at £500 + VAT, fixed in writing after a free diagnosis. In most cases you only pay if we recover your data.

One of these, from start to finish.

NG · NTG-2026-1996ON THE LOG ✓

A two-bay box that had run on one disk since the spring

An engineering firm based in Ilkeston called us because their office box stopped presenting its data volume. Several months beforehand, one member had dropped out behind a door nobody ever opens, leaving an amber light as the only sign it had failed. Since then, the remaining member had been running the volume single-handed, and was beginning to fail itself. Each disk was imaged alone; the worn disk took two nights of short passes. Blocks refused by the worn disk were picked up from its older partner, and blocks the older partner had missed came from the newer side. All 20 years' worth of drawings, plus the job ledger, were opened on the bench before the parcel went back. Three days, door to door.

The two members cloned one at a time3 days between arrival and return

What helps, and what does damage.

Worth doing first

  • Shut off power to the box and leave it off
  • Post every member, the dead one included
  • Number each disk to its bay before pulling it
  • Tell us whether a rebuild or a re-sync has run

What makes it harder

  • Letting it re-sync onto a replacement disk
  • Reactivating a Windows mirror marked Failed
  • Turning repair utilities loose on either member
  • Posting one disk and keeping the other at home

Answers before you spend anything.

One disk is still running. Why do you want the other?

A mirror leaves you holding two versions of the same volume, and those versions almost never remain identical. Often, blocks refused by one side can be copied cleanly from the other. A member may also be weeks out of date, having quietly left the set before anyone checked the front panel. Put both clones on a bench and each block can be taken from the side that still reads it, at the date you actually want; no striped set offers that option. So: the pair, bay numbers marked, and the disk your box has marked as dead.

The box wants to rebuild onto a fresh disk. Should I let it?

No. Of everything on this page, this decision causes the most damage. A rebuild copies one member across the other in a direction the controller decides for itself. If the disk you were left with turns out to be the failing one, or merely the older one, your good side gets overwritten and no other version of it survives anywhere. Cut the power, leave every disk in its bay and take clones first. After that, nothing anyone presses can undo them.

I deleted a folder and it vanished from both disks. Is a mirror not a backup?

It is not, and treating one as a backup is the most common misunderstanding this bench meets. Every write goes to both members at the same moment, so a deletion, a corrupt write or encryption by ransomware lands on both sides identically. One disk failing is the only failure protected against. Any data that hasn't been overwritten can still be recovered, which is why you should unplug your box straight away and not wait until the weekend.

What do I send, and what will it cost?

RAID, NAS and server jobs start at £500 + VAT. A free diagnosis comes first, and one price is agreed in writing before any chargeable work begins. Get a quote first, by phone on 0115 8220606 or with our quote form. Include all members of the set (bay number noted on each), the disk the card marked as dead as well, and let us know what has been attempted already. If the disks will not come out of a network box, please send the entire box. Bare disks removed from a server chassis or desktop enclosure travel in antistatic bags. There is no collection service and no counter in Nottingham. Post it insured and tracked to our intake lab at Manchester Data Recovery, Peter House, Oxford Street, Manchester M1 5AN, or drop it off there (no appointment needed) Monday to Friday, 9am to 5:30pm.

Start here if the same thing is happening to yours.

When the server will not start → Asus and HP laptops → Server and RAID work → The full device list →

Switched off, a drive cannot get any worse.

The look costs nothing. It gives you a file listing of what opened and what did not, along with the cost of finishing the job, in writing, before anything chargeable begins. In most cases you only pay if we recover your data. Do not switch the drive on until you have that listing.

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Get a quote, then send it Posting it to Manchester