RAID adds redundancy and sometimes performance to server storage. RAID 1 mirrors; RAID 5/6 use parity; RAID 10 combines mirroring and striping. Choose by capacity, rebuild time, and I/O needs. RAID is not a substitute for backups.
RAID levels at a glance
- RAID 1: Mirror of two (or more) disks. One disk can fail; capacity is half. Simple and robust.
- RAID 5: Striping + parity; one disk can fail. Good balance of capacity and redundancy; rebuild can be slow on large arrays.
- RAID 6: Like RAID 5 but two parity blocks; two disks can fail. Safer for large volumes.
- RAID 10: Mirroring + striping. Best read/write performance and redundancy; capacity is half. Often used for DB and critical I/O.
What to consider
- Capacity: How much usable space do you need after redundancy?
- Rebuild time: After a disk fails, how long until the array is safe again? Large RAID 5/6 can take hours.
- I/O: RAID 10 is best for random I/O; RAID 5/6 for sequential or capacity-focused workloads.
Summary
RAID 1 = mirror; RAID 5/6 = parity; RAID 10 = mirror + stripe. Choose by capacity, rebuild time, and I/O. Always combine RAID with backups (RAID is not backup).
