RAID 10 and RAID 5 are the two levels most people weigh up when they want both capacity and protection from a failed disk — and on paper they can look similar. In practice they behave very differently when a drive dies, when the array rebuilds, and when you’re writing a lot of data. Here’s a plain comparison of how they differ, and which one fits which job.
RAID 5 spreads data and parity across disks for maximum capacity. RAID 10 mirrors pairs of disks and stripes across them for speed and safer rebuilds. The trade-off is capacity versus write performance and rebuild risk.
RAID 5 stripes your data across three or more disks and adds parity — extra information, spread across all the drives, that lets the array reconstruct the contents of any single disk that fails. Its appeal is efficiency: you lose only one disk’s worth of space to protection, so a four-disk RAID 5 gives you three disks of usable capacity. That makes it popular for file servers and NAS boxes where storage space and read performance matter and budgets are finite. The catch is what happens when a disk fails, which is where RAID 5 and RAID 10 part ways.
RAID 10 (sometimes written 1+0) takes a different approach: it pairs disks into mirrors — each disk in a pair holds an identical copy — and then stripes data across those mirrored pairs. You need at least four disks, and you lose half your total capacity to the mirroring, so a four-disk RAID 10 gives you two disks of usable space. In return you get excellent read and write performance, and — crucially — a much simpler, safer recovery when a disk dies, because the array just copies from the surviving mirror rather than recalculating parity across every drive.
This is the distinction that matters most. When a RAID 10 disk fails, its mirror partner still has a complete copy, so rebuilding onto a replacement is a straight disk-to-disk copy — fast and low-stress on the other drives. When a RAID 5 disk fails, the array must read every remaining disk in full and recalculate the missing data from parity — a slow, intensive process that hammers drives which are often the same age and mileage as the one that just died. If a second disk throws an error during that rebuild — an unreadable sector is enough — a RAID 5 rebuild can fail and take the array with it. It’s the classic failure mode behind our guide on what to do when a RAID won’t rebuild.
For read-heavy storage where capacity per pound is the priority — media libraries, archives, general file shares — RAID 5 is efficient and sensible, provided you back it up and don’t run it on tired old disks. For anything write-intensive or business-critical — databases, virtual machines, busy shared storage — RAID 10’s faster writes and far safer rebuilds usually justify the lost capacity. Larger arrays sometimes use RAID 6 (two parity disks) as a middle ground. Whichever you run, if it does fail, don’t force a rebuild — both levels are recoverable when imaged and rebuilt offline, and RAID recovery starts from £500 +VAT.
RAID 5 stripes data with parity across three or more disks, losing only one disk of capacity to protection, which maximises usable space. RAID 10 mirrors pairs of disks and stripes across them, losing half the capacity but giving faster writes and much safer rebuilds. In short, RAID 5 favours capacity, RAID 10 favours write performance and rebuild safety.
Neither is universally better, it depends on the job. RAID 5 suits read-heavy storage where capacity per pound matters, like archives and file shares. RAID 10 suits write-intensive or business-critical systems like databases and virtual machines, where its faster writes and safer rebuilds justify the lost capacity. Both need a separate backup regardless.
Because rebuilding a failed RAID 5 disk means reading every remaining disk in full and recalculating the missing data from parity, an intensive process that stresses drives often the same age as the one that failed. If a second disk hits an unreadable sector during the rebuild, the rebuild can fail and take the whole array with it. RAID 10 avoids this by copying from a surviving mirror.
RAID 5 can survive one disk failure; a second failure before the rebuild finishes loses the array. RAID 10 can survive one disk per mirrored pair, so in a four-disk array it can sometimes survive two failures, but only if they are in different pairs. If both disks in the same mirror fail, that array is lost.
Usually, yes, if handled correctly. Both levels are recoverable by imaging every disk read-only and rebuilding the array offline from the copies. The key is not to force a rebuild or re-initialise the array after a failure, which can overwrite the data. RAID recovery starts from 500 pounds plus VAT after a free diagnostic.
If a disk has failed, power the array down and send the drives labelled in order. We rebuild it offline from read-only images — free diagnostic, fixed quote first.