NDR / Every kind of NAS / Two-bay NAS

DS224+ · TS-264 · My Cloud EX2 · LinkStation Duo · ReadyNAS 212

Two-bay NAS data recovery. A mirror is two chances, and the second one is usually spent on the resync.

A two-bay NAS holds two drives joined one of three ways: a mirror, where each drive is a copy of the other; SHR or RAID 1, which on two drives is the same thing; or RAID 0, where the data is striped across both and neither means anything alone. Most are mirrors, and a mirror fails in a particular way: one drive dies, the unit carries on, the owner fits a new drive, and the resync reads every sector of the survivor, which was the same age and had the same life, and finds the bad sectors it had been quietly working around. A two-bay set is £500 + VAT upwards after the free look, fixed in writing, 5–10 days at the bench.

Free first lookOne fixed figure in writingNo data, no bill on most jobsReturn postage paid

Rather talk it through? An engineer answers the bench line
0800 6890668

Power it down. Label each drive with its bay number. Do not rebuild, repair, initialise, reinstall or reset. A rebuild reads every sector of every surviving drive, and on a set with a second weak member it finishes what the first failure began. Nothing on the drives gets worse while the unit is off.

Two-bay symptoms, and how long each gives you.

Not listed? Describe it on the form →

One drive light red, the shares still thereA degraded mirror. Copy what matters, then power down. Do not fit a new drive.Do not delay

The resync stalled or the unit rebooted mid-rebuildThe survivor has bad sectors. Power down now.Do not delay

Both drives failed within weeksThe same batch, the same life. Both go to the bench.Do not delay

RAID 0 and one drive is deadNeither drive means anything alone. The dead one is imaged first.Do not delay

The wrong drive was pulled and the unit now wants to rebuildStop. Power down; the freshest drive is worked out from the metadata.Do not delay

Packing it and posting it: power the unit down, write the bay number on each drive with a marker before it comes out, and send every drive from the set, including any SSD cache. Each drive travels in an anti-static bag inside its own padding, in a box with nothing able to move; the unit itself comes too if it holds an encryption key or a proprietary layout, and its power supply with it. Insure the parcel for what the files are worth rather than the price of the drives, and use a tracked service. The posting address is not printed anywhere on this site; it arrives by email in reply to the form, with a booking sheet to print; the sheet inside the parcel is what matches it to your enquiry when it is opened. Or hand the sealed parcel in at the nearest of ten drop-off points, your name on the outside and the sheet inside; say where you are on the form and it comes by email. We pay the postage home either way. The whole of it is written up on the guide to packing and posting.

How it is laid out, and what fails.

The mirror, and the resyncEach drive holds a full copy plus mdadm metadata with an event count. A resync reads every sector of the survivor to write the new drive; the survivor's bad sectors stop it. On the bench both drives are imaged and the freshest copy chosen from the metadata.

SHR on two drivesSynology Hybrid RAID on two equal drives is a mirror with LVM on top. On two unequal drives the extra space on the larger one is a separate Basic volume, which surprises people when the small drive dies.

RAID 0 on two drivesChosen for speed and capacity, and the loss of one member is the loss of the volume until that member is imaged and the stripe reassembled from the two images.

The units themselvesDSM, QTS, WD OS 5, Buffalo and ReadyNAS all sit on a mirrored system partition across both drives, which is why a two-bay unit can boot with one drive out, and why a failed update takes the system partition and not the data.

What it says, and what it means.

Describe yours to us →

What you see	The usual reason for it	Where that leaves you
Degraded; volume still readable	One member lost; redundancy gone	Copy critical files, then power down; no new drive
Rebuild at n per cent, then stopped or rebooted	Survivor's bad sectors	Power down; both imaged; freshest copy used
Volume crashed after a rebuild attempt	Second member lost mid-resync	Set rebuilt from the images and the metadata
RAID 0: volume missing	A member failed	Failed member imaged; stripe reassembled
Both drives marked failed	Same-batch failures, or a controller fault	Each drive assessed on the bench

From the box arriving to your files going back.

Work we have closed →

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

A case number goes on the parcel and a number on every drive the day it is opened, and an engineer settles what has actually happened before anything spins. The unit is examined on its own; each drive is assessed on our own equipment, never in a NAS that will try to rebuild. 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 writingNo rebuilds, no repairs, no resets

The unit, and the drives, apart

On a two-bay unit the first question is which drive is the freshest, and the answer is in the mdadm metadata, not in the unit's opinion. Both drives are read on the bench; the one that dropped out first has a lower event count and is used only for the areas the other cannot read.

Unit and disks assessed separatelyFailing members to the clean bench

Every member imaged, once

Nothing is worked on live and nothing is rebuilt on the originals. Every drive in the set is imaged sector by sector, the weak ones head by head with the bad areas last, and the SSD cache with them where there is one. From then on the originals are not touched again.

Every drive, including the cacheWeak areas last

The set put back together, from the images

Order, chunk size, parity rotation and the reshape point are read from the drives' own metadata and the array is reassembled in software: mdadm and LVM under SHR, X-RAID and QTS pools; a ZFS pool imported read-only; Drobo's BeyondRAID zones reconstructed. The file system, Btrfs, ext4, XFS or ZFS, is repaired on the virtual volume, and encrypted volumes are unlocked there with the key you supply. Never on the originals.

Rebuilt in software, from imagesThe file system repaired on the virtual volume

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 at all. 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 opened the files on a machine of your own.

No charge until you accept the figureFresh media, supplied with the job5–10 days at the bench

What arrives most often

Do not fit the replacement drive. The resync is what finishes a mirror off, and it cannot be paused once the survivor's bad sectors are found.
Two drives bought together fail together. Same batch, same hours, same heat. A mirror whose first drive died is a mirror whose second is on notice.
Copy what matters while it is still readable, if the unit is still serving files. Then power down. Do not copy everything; the survivor's bad areas are the ones it will hit.
The event count tells the truth about which drive dropped out first, and the bench reads it before anything is assembled.

How much comes back: from a degraded mirror that was powered down, usually all of it. From a mirror that was asked to resync with a weak survivor and then reset, less. The difference is nearly always the rebuild.

One job, followed all the way through.

UK · NDR-2026-0533JOB LOGGED ✓

A Synology DS220+ in SHR whose owner fitted a new drive and watched the resync stop at 41 per cent

The survivor had bad sectors the unit had been working around for a year, and the resync found them. The owner powered down, which mattered. Both original drives were imaged on the bench, the survivor slowly with its weak areas last, the dropped drive read for the stripes the survivor could not give, and the Btrfs volume mounted from the merged image. Everything came back.

100% of it recovered6 days here, and back by post

Illustrative example — replace with a genuine case

What helps, and what harms.

Do this much first

Power it down when the first drive fails, once the critical files are copied
Write the bay number on each drive
Send both original drives, not the replacement
Tell us the RAID mode and the DSM or QTS version

What sets us back

Fitting a new drive and letting it resync
Pulling a drive to see which one is bad
Clicking Repair, Remove or Manage on the pool
Moving the drives to another unit

Questions answered before you commit.

One drive in my two-bay NAS has failed. Is my data safe?

On a mirror, yes, for now: the survivor holds a full copy. What puts it at risk is the resync with a new drive, which reads every sector of a survivor that has had the same life as the drive that died. Copy what matters, power down, and send both.

Should I replace the failed drive and rebuild?

Not until the data is safe elsewhere. If the survivor has bad sectors the rebuild stalls on them, and a degraded mirror becomes a failed one.

I pulled the wrong drive. Is it gone?

No. Power down and do not let the unit rebuild. The metadata on each drive records which dropped out when, and the bench assembles from the right one.

What does it cost?

A two-bay set is £500 + VAT upwards after the free look, fixed in writing, whatever the mode.

How long does it take?

5–10 days at the bench for most two-bay sets.

Begin here if yours is doing the same thing.

Synology storage pool degraded →Four-bay RAID 5 and 6 →Synology →QNAP →WD My Cloud →

Nothing gets worse while it is powered down.

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 unit off and the drives in their bays.

0800 6890668

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