RAR / Every level and layout / RAID 10

RAID 10 · RAID 1+0 · RAID 01 · mirror pairs · near · far · offset · PERC · Smart Array

RAID 10 data recovery. Mirrors striped together: safe against one failure per pair, and not against two in the same pair.

RAID 10 stripes data across mirror pairs, so that every block exists on two drives and the set tolerates one failure in each pair; RAID 01 mirrors two whole stripe sets, and tolerates the loss of one set. Both are fast and both are common in database servers, where they arrive here for one reason above all: both halves of a pair failed, usually because the first failure was not noticed and the pair kept the same hours. The bench needs to know which drives were pairs, which copy in each pair is the newest, the stripe size and the order of the pairs; on mdadm it also needs the layout, because near, far and offset put the copies in different places. A RAID 10 of four members 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 down. Label every slot before a drive comes out. Do not rebuild, do not force a drive online, do not import or clear a foreign configuration, do not initialise, and do not run chkdsk, fsck, zpool import -F or mdadm --create on the members. A rebuild reads every sector of every survivor and writes to the replacement; each of the commands writes to the drives. On images, all of them are reversible. On the originals, none of them is.

RAID 10 symptoms, and how long each gives you.

Not listed? Describe it on the form →

Degraded, one member outThe pair's other half is carrying the load alone. Image it before any rebuild.Do not delay

Both drives of one pair failedThe set is offline. Both are imaged; the newest copy of each stripe used.Do not delay

Rebuilt the wrong wayA stale half copied over the current. Stop; the current data may survive on the source.Do not delay

Foreign after a controller swapThe pairing is in the metadata. Do not clear.Do not delay

Volume corrupt after a rebuildA stale mirror, or the pairing guessed wrong. Stop writing.Do not delay

Two members from different pairs failedStill readable. Copy what matters, then image.Everyday job

Packing it and posting it: power down, photograph the controller's screen or export its log, and write the slot number on each drive with a marker before it comes out of its carrier. Send every member of the set, including the one that failed first; it holds the stripes the rebuild never reached. Each drive travels in an anti-static bag inside its own padding, in a box with nothing able to move. Send the controller if it was replaced or holds an encryption key; otherwise it stays. Insure the parcel for what the data is worth, use a tracked service, and know that 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.

What it tolerates, what fails it, and what the bench has to find.

Pairs, not just membersLosing two members is fine if they are in different pairs and fatal if they are the same pair. The metadata says which is which; where it was cleared, identical content at the same offset says it.

The newest copyA mirror half that dropped out and was forced back is stale. The controller's event counts say which half is current; the bench reads them from each member and uses the current half, with the stale one only to fill holes.

Near, far and offsetmdadm's RAID 10 puts the copies of a block next to each other (near), in the other half of the set (far) or one stripe along (offset). The superblock records the layout; guessed wrong, half the reads are from the wrong place.

RAID 01A mirror of two stripe sets. Lose one drive and its whole stripe set is out; the other set carries everything. It is recovered as a RAID 0 with a spare copy of every stripe.

What a reconstruction has to determine.

Describe yours to us →

Unknown	Where it is read from	What goes wrong when it is guessed
Pair membership	Metadata; identical content at the same offsets	Two unrelated drives treated as a mirror
Newest copy per pair	Event counts; timestamps in the file system	Stale data assembled into current files
Stripe size and pair order	Metadata; entropy and file-system anchors	Files interleave across pairs
mdadm layout	Superblock (n2, f2, o2)	Half the blocks read from the wrong drive
Data offset	Metadata; member 0's structures	The volume start is missed

From the parcel 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 member the day it is opened, matched to the slot you wrote on it. Each member goes on the imager its interface needs, never on a controller, and its metadata is read before a sector is: the level, the order, the stripe size, the event counts that say which member is current and which dropped out first. An engineer settles what has happened to the set and how much of it can honestly be read back. 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 imports, no initialise

Every member imaged, including the one that failed first

Every drive in the set is imaged sector by sector, weak areas last, on hardware that controls every retry, with a map of what could not be read kept for each. Members with failed heads go to the clean bench first; that is the drive site's work and the same bench does it. The drive that dropped out first is imaged too, because it still holds every stripe written before it dropped, and a rebuild that stalled part-way never reached them.

Sector by sector, weak areas lastThe first-dropped member included

The geometry, from the metadata or from the parity

Where the controller's metadata survives on the members, the order, stripe size, parity rotation and data offset are read from it. Where it was cleared or overwritten, they are recovered from the data: parity across the members at the same offset should XOR to zero on a consistent stripe, which confirms the level and finds the stale member; where parity lands says the rotation; entropy at stripe edges and the file system's own anchors give the stripe size, the order and the start.

Metadata first, parity secondOrder, stripe, rotation, offset

Assembled in software, and repaired on the virtual volume

The set is put together from the images in software, with nothing written to any of them: the current members in, the stale member used only to fill holes a survivor could not give. The file system is checked and repaired on a copy of the virtual volume, VMFS and CSV volumes opened and the virtual machines' disks extracted, databases repaired where they need it. The originals are not touched again.

Nothing written to the imagesVirtual machines and databases opened

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

A degraded RAID 10 is one drive from its pair being gone. The surviving half of the pair is the only copy of its stripes; image it before anything rebuilds onto a replacement.
Rebuilding the wrong direction happens. A stale drive reinserted and the controller told to rebuild the pair from it. Stop at once; the source may still hold the current data.
Send all four, even where two are fine. The pairing is proved on the bench from all of them.
On mdadm, the layout is in the superblock. --examine on any member says n2, f2 or o2, and the bench reads it from the image.

One job, followed all the way through.

UK · RAR-2026-0603JOB LOGGED ✓

A four-drive RAID 10 on a Smart Array P440ar holding a SQL Server instance, one half of a pair failed in March and the other half in June, unnoticed until the logical drive went offline

All four drives came in. Both halves of the failed pair were imaged, the June drive after a head swap on the clean bench and the March drive directly; its data was three months stale. The pairing and stripe were read from the RIS metadata, the set assembled from the two healthy members and the June image, and the March image used only for stripes the June drive could not read. The database was repaired from its log and copied out.

99.99% of the database recovered7 days here, and back by post

Illustrative example — replace with a genuine case

What helps, and what harms.

Do this much first

Power down and label the slots
Send every member, including the one that failed months ago
Tell us which slot failed first, and when
Export the controller log

What sets us back

Rebuilding onto a replacement with the pair's other half unimaged
Rebuilding the pair from the stale drive
Clearing the configuration after a controller swap
Assuming two failures means the data is gone

Questions answered before you commit.

Both drives of one mirror pair failed. Is the data gone?

Usually not. Both are imaged, the newer one's data used, and the older one's stripes used only to fill what the newer cannot read. The other pairs are fine.

Is RAID 10 easier to recover than RAID 5?

When the failures are in different pairs, much easier; there is a full copy of everything. When both halves of one pair fail, it is a two-drive imaging job with a decision about which copy is current.

What is the difference between RAID 10 and RAID 01?

RAID 10 stripes across mirror pairs; RAID 01 mirrors two stripe sets. They tolerate different failures and are recovered differently, and the metadata says which yours is.

What does it cost?

£500 + VAT upwards for four members after the free look, fixed in writing; larger sets from £1,250 + VAT.

How long does it take?

5–10 days at the bench for a set of four.

Begin here if yours is doing the same thing.

Virtual machine, VMDK and VHDX recovery →RAID 1 →RAID 0 →mdadm and LVM →HPE Smart Array →

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 server off and the drives in their slots.

0800 6890668

Price my job Packing and posting

Every level and layout

Manufacturers

Whatever it is saying now

Servers

What it costs, and what follows