Most arrays that arrive here were recoverable when they failed and less recoverable by the time they were sent. The damage is almost never the original fault — it is what happened in the hours afterwards.
Every level has its own arithmetic, but the sequence is identical: power down, preserve bay order, image every member read-only, then reconstruct from the copies. Only the reconstruction differs by level.
Power down and leave it down. A degraded array running is a degraded array getting worse, and on a set with spreading bad sectors every hour of use costs reads you will want later. Preserve bay order. Label each disk with the bay it came from before removing it; disk order is central to every reconstruction and guessing it costs time and money. Never write to the members. No rebuild, no resync, no initialise, no repair utility, no re-creating the array “to see if it mounts”. Image before anything else. Every member is cloned read-only, and all reconstruction happens against the copies so nothing you try can close off a later option.
RAID 0 has no redundancy at all, so every member is required and the outcome tracks the condition of the failed disk — covered in full on our RAID 0 recovery guide. RAID 1 gives you two copies to merge into one good image, which makes it the most winnable level and the easiest to ruin with a careless rebuild — see the RAID 1 guide.
RAID 5 survives one lost member by computing it back from parity; it fails when a second member drops, or when bad sectors on the survivors mean a stripe cannot be resolved even though all disks are nominally present. RAID 6 carries two parity blocks and so tolerates two failures, which usually means the arrays that reach us have lost three, or have parity that no longer verifies. RAID 10 is mirrored pairs that are then striped, so there is no parity to compute — the work is establishing which disk pairs with which, and it survives multiple failures provided they are not both halves of the same pair.
Controller metadata is treated as a hint rather than a fact, because a controller that has failed or been reset is exactly the thing that cannot be relied on. Stripe size, member order, parity rotation and data offset are all derived from the disks themselves — candidate configurations are tested until reassembly produces coherent file-system structures instead of noise. The array is then assembled virtually from the images, and the file system rebuilt from that.
Where a member needs physical work first — donor heads, a board repair, firmware attention — that happens before imaging, because a disk that will not respond cannot contribute to the reconstruction at all.
Send every disk, including any that were already marked failed — a disk the controller ejected often still holds readable data and can be the difference between partial and full recovery. Label them by bay. Tell us the controller or NAS model, the RAID level if you know it, and crucially what has already been tried; a rebuild that was started and abandoned changes the approach entirely, and it is far better to say so than to have it discovered.
RAID, NAS and server recovery starts from £500 +VAT, fixed in a written quote after a free 48-hour diagnostic. Where members need drive-level physical work we take a 50% deposit, with the balance payable only on a successful recovery.
Power it down and leave it down, then label each disk with its bay number. Don't let a rebuild, resync or repair run, and don't re-create the array to test it. Almost every unrecoverable array we see was recoverable at the moment it failed and was damaged by what happened next.
Often, yes — it depends on whether the second disk failed completely or simply dropped out. A disk the controller ejected is frequently still largely readable, and if its data can be imaged the array can be reconstructed. Both disks come in, both get imaged, and the reconstruction runs from the copies.
Only if every remaining member is genuinely healthy. A rebuild writes to the disks, and on an array with bad sectors it can write incorrect data where parity could not be read — which is the commonest way a recoverable array becomes an unrecoverable one. If the data matters more than the uptime, image first.
Yes, including any already marked as failed. Every level except RAID 1 needs the full set to reconstruct the volume, and even an ejected member usually contributes readable data. Label them in bay order before removing them.
RAID, NAS and server recovery starts from £500 plus VAT, confirmed in a written quote after a free 48-hour diagnostic. Where a member needs physical drive-level work there is a 50% deposit, with the balance due only on a successful recovery.