RAID 1, 5, 6 or 10 — capacity, resilience and performance
Do not choose RAID by capacity alone. Failure combinations, rebuild time, write workload and restore capability all matter.
RAID combines disks for resilience, performance or a larger storage space. Each level balances these goals differently, and nominal disk capacity is not the capacity available to data.
Before choosing, define acceptable downtime, maximum data loss, write workload, disk size and where an independent backup will be kept.
RAID 1 and RAID 10
RAID 1 mirrors data across at least two disks. It is simple and predictable but uses only part of total capacity. RAID 10 combines mirroring and striping for strong performance and relatively quick rebuilds at the cost of half the raw capacity.
- RAID 1 suits small two-disk systems.
- RAID 10 requires at least four disks.
- Surviving two failures in RAID 10 depends on which disks fail.
RAID 5 and RAID 6
RAID 5 distributes single parity and tolerates one disk failure. RAID 6 uses dual parity and tolerates two, with a larger write penalty and capacity cost equal to two disks. With large drives, rebuild duration and the chance of another error matter more than raw efficiency alone.
RAID is not backup
An array does not protect against accidental deletion, ransomware, application corruption, theft, fire or complete controller failure. A backup must be logically independent, tested and retained according to recovery objectives.
- Calculate usable capacity before purchase.
- Plan a spare drive and SMART/RAID alerts.
- Test the replacement and rebuild procedure.
- Perform regular restore tests from backup.
Before choosing a RAID level
- Calculate usable capacity and reserve space.
- Define tolerated failure count and combinations.
- Consider write workload and rebuild time.
- Design an independent, tested backup.
Put it into practice
Compare RAID levels
Enter disk count and capacity to compare usable space and the characteristics of common RAID levels.
Compare RAID levelsFrequently asked questions
Which RAID level is best?
There is no universal best. RAID 10 often wins on performance and rebuild simplicity, RAID 6 offers dual-disk resilience with more drives, and RAID 1 is a practical two-disk choice.
Can RAID use drives of different sizes?
Classic RAID normally limits each member to the smallest drive's capacity. Some platforms provide flexible proprietary layouts that must be evaluated separately.
Does RAID make writes faster?
It depends on the level, controller and workload. RAID 10 commonly scales writes well, while parity RAID pays for parity calculation and extra operations.