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ADR / Media and machines / RAID 1 mirror sets

Mirror sets · two disks, one volume

RAID 1 data recovery, London. A mirror is two disks that have drifted apart. Post both; the volume comes from the better of each.

RAID, NAS and server work starts at £500 + VAT here, and the diagnosis that settles the figure is free. In theory a mirror puts every block on both disks, so either one carries the whole volume. In practice the sets arriving here are the ones the theory does not cover: a pair out of one carton ageing at one rate, a controller laying identical corruption on both sides, a re-sync run in the wrong direction, plus the box which shed a member in March and has run on one disk since. Every member is cloned separately, read-only. Those clones are then compared, block for block, and the volume put together from whatever each side can still stand behind, the newer reading preferred where the two differ. Sets arrive by post from Islington, Barnet, Lewisham and Bromley, and your own disks go home with nothing written to them.

On most jobs: no data, no bill A free look first, then one figure in writing Media posted in from Croydon, Ealing and Camden

Put it to an engineer — the first look costs nothing
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RAID 1: what the symptom usually means.

Different fault? Try the finder →
What is going onThe usual reason for itWhere that leaves you
The NAS reports the volume as degradedOne member has gone. The disk still in the bay is holding the whole volume by itselfCopy off what you can, then post both
Both disks have got slower, and both went in togetherMirrored members clock the same hours, so wear tends to arrive on both at onceCut the power to the box now
A new disk went in and the side that read went emptyThe set re-synced in reverse, so the failing disk was copied onto the healthy oneStop now, and post both disks
The same folder has gone from both membersEvery write lands on both sides at the same instant, the bad ones includedRefuse the re-sync
The amber light went unnoticed until this weekThe mirror has run on one disk ever since, with nothing standing behind itPost both, not only the failed one
Windows marks the mirror Failed RedundancyA member has been dropped by the set, and quite often neither disk is at faultLeave it alone: no reactivate, no import
Packing it and posting it:a damaged drive is finished off by movement, so use a rigid box and pad it out. Declare the parcel at what the files are worth to you, not at what the disk cost, then send it tracked to our intake lab. We meet the cost of the trip home. Rather have the packing checked over before you tape the box up? Ring first. It is all set down on theguide to packing and posting.

One failure is all a mirror covers. Here is the rest.

Two-bay NAS boxes running as mirrorsA Synology, a QNAP or a bare two-bay enclosure, set up on the day with the safer of the two options. Underneath is Linux software RAID, which records the mirror onto the disks and not into the chassis — so the box itself can stay where it is. Send it whole, though, if you would rather not take the lid off.
Boot pairs and controller mirrorsThe boot pair under a small server, mirrored on a hardware card or by the Intel RST built into its board. In both cases a record of the set goes onto the disks themselves, and it reads back out of clones without the card and without the machine that held it.
Storage Spaces, mdadm and ZFSA mirrored dynamic volume or a Storage Spaces mirror on Windows; an mdadm pair under Linux; two disks running as a ZFS or btrfs mirror in a NAS. Each writes its own layout onto the members, each assembles above clones, and each has its own rule for choosing which member to believe — the very question at issue once one goes wrong.
Why rebuilding can worsen itWith parity, a rebuild can calculate the disk that is absent. A mirror calculates nothing: one member is simply laid over the other, whichever way the card decides. Choose wrong and your only sound copy is gone by teatime. On this bench the same work is done on clones, where taking a wrong turn costs an afternoon.

From the box arriving to your files going back.

Work we have closed →
01

Logged the day it lands, and the first look costs nothing Free

A case number goes on it the day the parcel lands, and an engineer settles what has truly failed before anything else happens — free of charge, and first in the order of work. Back to you come two things together: a straight note of what is liftable and what is not, plus one figure, fixed and written down. Accept it, or decline and owe us nothing.

Nothing to pay for lookingA single figure, put in writingNothing owed at this stage
02

Each disk cloned on its own

Behind a write blocker, each member is copied from end to end, and no file is opened until that copying finishes. The member that never failed gets exactly the care the failed one gets, because on a mirror half of what goes home comes off it. Ground that reads badly is saved until last and worked in short passes. Your own disks go back with nothing written to them.

Your disks are read, never writtenEach member read by itself
03

The pair of copies compared

Where the sides disagree, something has to decide which one to trust. Each member records the date of its last write in its own metadata; where metadata cannot settle it, the file systems on the clones can. Readable beats unreadable and newer beats older, and every one of those decisions is written down for you instead of being assumed.

The newer side establishedWeighed side by side, not assumed
04

The volume rebuilt above the clones

With that settled, the volume is reassembled over the copies, with its file system mended on those copies and not on the disks you sent. Files then get opened rather than counted: accounts, shared folders, databases, photographs. A filename on a listing is evidence of nothing. Whatever returns damaged is recorded as damaged.

Files opened, never merely countedDamage recorded file by file
05

You see the file list before you pay

What was recovered is listed for you first, and only then does a bill exist. Approve the list and it is invoiced; turn it down and it is not — and where nothing has come back, most jobs carry no charge whatever. Recovered data travels home on fresh media bought in for your job, with the postage at our end. Your case is not closed until you have read those files on a machine of your own.

No charge until you accept the figureFresh media, supplied with the jobThe post home is ours

What arrives most often

  • A mirror was never a backup — both disks take each write at the same moment, so a deletion, a corrupted save or a ransomware run is duplicated with equal fidelity. One disk giving out is the single event it covers. Worth having, certainly, and that is the whole of what it gives you.
  • Disks bought as a pair tend to fail as a pair — same batch, same shelf, same cabinet, same running hours. The second member frequently follows the first within weeks, so a degraded mirror buys less time than owners imagine, and whichever disk is still in the bay need not be the sounder of the two.
  • The direction of a re-sync decides everything — one member is laid over the other, and the card chooses which way round by rules of its own. Most of the bad jobs arriving here opened with a failing member being copied onto a healthy one, or a stale member onto a current one. If your box has offered to rebuild, decline and telephone before anything else gets pressed.
  • Send the disk the box refuses — frequently it is that member which holds the newer data, and frequently it will still clone. Hold it back and half the job has gone before it begins; occasionally all of it has.

What cannot be done: storage is the whole of this bench's work. Mirrors are the subject here — two disks in a network box, two in a desktop enclosure, two on a hardware card, a pair under Intel RST, a mirrored volume in Windows, an mdadm or ZFS set — arriving degraded, overwritten, or re-synced the wrong way round. Read both sides and the volume goes back together above the clones, your folders arranged as you kept them. Where the same ground has given out on both members, nobody can conjure those blocks back: certain files return with holes in them, and each is named in the report. Nor does anything written across come back. Encryption needs its key, and only you have it. No phones and no tablets. Prices open at £500 + VAT, fixed on paper once the free diagnosis is done, and on most jobs no recovered files means no invoice.

One job, followed all the way through.

LDN · ADR-2026-3396JOB LOGGED ✓

A two-bay unit that had been running on a single disk since spring

An engineering firm in Ealing telephoned when the office box would no longer present its data volume. Behind a door nobody opens, a member had dropped out months before, an amber light its only announcement, and the disk left standing had carried the volume by itself ever since — and was beginning to go the same way. Each was imaged on its own, the tired one across two nights of short passes. Whatever that disk would not give up was read off its older partner, and whatever the older partner could not manage was read from the newer side instead. Twenty years of drawings and the job ledger were opened here before the parcel travelled back. Three days, door to door.

The pair ofmembers cloned separately3days here, and back to you

What helps, and what harms.

Do this much first

  • Pull the power and leave the box off
  • Post every member, the failed one included
  • Mark each disk with its bay number before pulling it
  • Say whether a rebuild or a re-sync has already run

What sets us back

  • Allowing a re-sync onto a replacement disk
  • Reactivating a Windows mirror flagged Failed
  • Pointing repair utilities at either member
  • Posting one member and leaving the other at home

Questions answered before you commit.

One disk still runs. Why do you want the other as well?

Because you are holding two versions of one volume, and they are almost never the same version. A block the first disk will not surrender frequently lifts straight off the second. A member may also be weeks stale, having slipped out of the set long before anybody glanced at the front panel. With two clones on a bench, every block can be drawn from whichever disk still reads it, and dated as you would want it — which no striped array can offer. So send the pair, mark the bays, and add the disk the box refuses.

The box offers to rebuild onto a replacement. Do I say yes?

No — and that is the single most damaging decision available on this page. A rebuild takes one member and lays it over the other, in a direction the controller picks by rules of its own. Should the disk still in the bay be the failing one, or merely the stale one, it is your good side that disappears underneath, and after that no second version exists anywhere. Power the box down, leave the disks where they sit, and get clones made first. Nothing anybody presses later can undo a clone.

A folder I deleted is gone from both members. Is a mirror not the same as a backup?

No, and expecting one to behave like a backup is the most frequent misunderstanding reaching this bench. Both members receive each write at the same moment: delete something, save something corrupt, or let ransomware run, and both copies carry it equally. The single event a mirror stands against is one disk giving out. Anything not yet overwritten stays recoverable, which is the argument for unplugging the box that day instead of leaving it until Saturday.

What has to be sent, and what is the price?

£500 + VAT is where RAID, NAS and server work begins. Diagnosis before that is free, and the fixed figure following it is written down and agreed by you before anything chargeable happens. Send every member with its bay number on it, add the disk the card refuses, and describe whatever has already been attempted. Not keen on opening the chassis? The network box can travel whole. Disks lifted out of a server chassis, or out of a desktop caddy, go bare in antistatic bags. No collection service runs and there is no counter to visit, so use an insured, tracked parcel to the intake lab — the address is on our contact page.

Begin here if yours is doing the same thing.

Servers that refuse to come up → Toshiba laptop drives → RAID and server jobs → Every device we take →

Nothing gets worse while the power is off.

Looking at it is free. Back comes a list of what opened and what did not, together with a single price to finish, set down in writing while you are still free to say no. On most jobs an invoice only follows the data. Until that list reaches you, leave the drive switched off.

0203 0868633

Get it assessed Sending it to Guildford