RAID 10 and RAID 5 are the two RAID levels most people weigh up when they want both capacity and protection against a failed disk, and on paper they can look similar. In practice, they behave very differently when a drive fails, during an array rebuild and while writing large amounts of data. Below is a simple comparison of how they differ, and which jobs each one best suits.
RAID 5 offers maximum capacity by spreading data and parity across multiple disks. RAID 10 creates pairs of mirrored disks and then stripes across these pairs 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: additional information, spread across all the drives, that allows the array to reconstruct the contents of any single disk that fails. Its appeal is efficiency: you only lose one disk’s worth of capacity to protection, so a four-disk RAID 5 gives you three disks of usable capacity. For this reason, it is commonly used for file servers and NAS boxes, where storage space and read performance matter and budgets are often limited. 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, meaning each disk in a pair holds the same information, and then stripes data across those mirrored pairs. You need at least four disks, and because they are mirrored, you lose half of your total capacity, so a four-disk RAID 10 gives you two disks of usable space. The trade-off for this loss of storage is excellent read and write performance and, above all, a much simpler, safer recovery when a disk fails, because the array just copies from the surviving mirror instead of recalculating parity across every drive.
This is the distinction that matters most. When a RAID 10 disk fails, its mirror partner still has a full copy of the data, so once you replace the failed disk, the rebuild is a direct disk-to-disk copy: fast, and with minimal stress on the other drives. When a RAID 5 disk fails, the array must read every remaining disk completely and reconstruct the missing data from parity, a much slower process that puts heavy wear on drives which are often the same age and mileage as the one that just died. If a second disk develops an error during that rebuild (an unreadable sector is enough), a RAID 5 rebuild can fail and take the array with it. It is the classic failure mode behind our guide on what to do when a RAID won’t rebuild.
For read-heavy storage where you want the most capacity per pound (media libraries, archives, general file shares), RAID 5 is efficient and makes sense, provided you have backups and do not run it on old, worn disks. For anything write-intensive or business-critical (databases, virtual machines, busy shared storage), RAID 10’s faster writes and far safer rebuilds normally justify the lost capacity. Larger arrays sometimes use RAID 6 (two parity disks) as a compromise. Whichever you run, if it does fail, do not attempt to force a rebuild: both levels are recoverable once they are imaged and rebuilt offline, and RAID recovery starts from £500 +VAT.
RAID 5 uses striping to spread data across three or more disks along with parity information, losing no more than one disk of capacity to protection, which maximises usable space. RAID 10 configures mirrored pairs of disks and then stripes across those pairs, losing half of the total capacity but providing faster writes and much safer rebuilds. In summary, RAID 5 favours capacity, whereas RAID 10 favours write performance and rebuild safety.
Neither configuration is inherently better; it depends on the job. If you need read-heavy storage where capacity per pound matters, such as archives and file shares, RAID 5 is likely the better choice. If your application is write-intensive or business-critical, such as databases and virtual machines, RAID 10’s faster writes and safer rebuilds justify the lost capacity. Both need a separate backup regardless.
Because rebuilding a failed disk in a RAID 5 configuration involves reading through all of the remaining disks in full and recalculating the missing data from parity. This is an intensive operation that stresses drives which are often the same age as the one that failed. If a second disk hits an unreadable sector during this process, the rebuild can fail and take the whole array with it. RAID 10 avoids this by copying from a surviving mirror.
RAID 5 will survive one disk failure, but it will lose the array if a second disk fails before the rebuild finishes. RAID 10 can survive one disk failure per mirrored pair, so in a four-disk array it may survive two failures, but only if they occur in different pairs. Once both disks in a single mirror have failed, the array is lost.
Usually, yes, if handled correctly. Both levels are recoverable by read-only imaging of every disk followed by a rebuild of the array offline from the copies. The most important thing is not to force a rebuild or re-initialise the array after a failure, as this can overwrite the data. RAID recovery starts from £500 plus VAT after a free diagnostic.
After a disk failure, please power the array down and send us the drives labelled in the correct order. We then rebuild it offline from read-only images, with a free diagnostic and a fixed price quotation first.