It is the level people choose when they want redundancy without the write penalty of parity — and the one that behaves most predictably when something fails, because there is no arithmetic to reverse.
Four disks become two mirrored pairs, and data is striped across those pairs. You lose half your raw capacity and gain fast writes and straightforward failure behaviour.
RAID 10 takes disks in pairs and mirrors each pair, then stripes data across those mirrors. With four disks you get two pairs; with eight, four pairs. Every block exists twice, on both members of whichever pair holds it, and consecutive blocks land on different pairs so reads and writes spread across the set.
The order is what distinguishes it from RAID 01, which stripes first and mirrors the stripes. RAID 10 is more resilient, because a single disk failure degrades only one mirror rather than an entire striped set — which is why RAID 10 is what almost everyone actually deploys.
RAID 5 uses parity, giving you the capacity of all disks but one — four 4 TB disks yield 12 TB against RAID 10’s 8 TB. That is the case for RAID 5, and it is a real one. Against it: every RAID 5 write requires reading old data and parity and writing both back, which is why write performance suffers under load.
The larger difference is rebuild behaviour. Rebuilding RAID 5 reads every sector of every surviving disk to recompute the missing member — hours of maximum stress on disks that are the same age as the one that just died. Rebuilding a RAID 10 pair copies from its mirror partner only, so the rest of the array is untouched and the exposure window is far smaller. On large modern disks that difference matters more than the capacity saving.
In an eight-disk RAID 10 you can lose up to four disks and keep running, provided no pair loses both members. Lose both halves of one pair and the volume fails immediately regardless of the other six. So the meaningful question after a failure is never “how many disks are down” but “are any two of them partners”.
This also makes RAID 10 comparatively benign for recovery: with no parity, reconstruction means identifying which disks pair with which and where each pair sits in the stripe, which is more tractable than parity work provided one member of each pair is readable.
Each disk is imaged read-only and the layout — pair membership, stripe size and order — derived from the data rather than trusted from the controller. Where both members of a pair are damaged, the two images are merged so that whichever copy read a given sector cleanly supplies it, which frequently produces a complete pair from two incomplete disks.
The thing not to do is let it resync onto a disk you have reinserted, or re-create the array to test it. RAID, NAS and server recovery is from £500 +VAT after a free 48-hour diagnostic and a written quote.
It mirrors disks in pairs, then stripes data across those pairs. Every block exists twice within its pair, and consecutive blocks land on different pairs so throughput spreads across the set. You use half your raw capacity and get fast writes with no parity calculation.
As many as one per mirrored pair — so an eight-disk array can survive four failures, provided no pair loses both members. Lose both halves of a single pair and the volume fails immediately, however many other disks are still healthy.
It depends what you are optimising. RAID 5 gives more usable capacity; RAID 10 gives faster writes and far safer rebuilds, because rebuilding a pair copies from its partner rather than reading every sector of every surviving disk. On large modern drives, rebuild exposure usually outweighs the capacity saving.
Usually, and often more readily than parity levels. With no parity to reverse, the work is identifying pair membership and stripe order from the disks themselves. Where both members of a pair are damaged, their images can be merged so each supplies what the other could not read.
RAID, NAS and server recovery starts from £500 plus VAT, fixed 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 payable only on success.