RAID 1 and RAID 5 solve the same basic problem — surviving a drive failure without losing data — using different mechanics. RAID 1 mirrors everything you write across two drives, so one is always a full duplicate of the other. RAID 5 spreads data and a calculated parity value across three or more drives, so any single drive can fail and be rebuilt from what remains on the others.
What changed in 2026
- Drive capacities kept climbing while rebuild speeds did not keep pace, meaning the window of vulnerability during a RAID 5 rebuild on large modern drives is longer and riskier than it was a few generations ago.
- RAID 10 became the more commonly recommended default for NAS units with four or more bays, since it offers faster rebuilds than RAID 5 at a similar capacity tradeoff, pushing straight RAID 5 toward more specialized use.
- More consumer NAS software started warning users explicitly about rebuild risk and urging a fresh backup before starting a rebuild after a drive replacement.
How RAID 1 works
Two drives, one mirror. Every write goes to both drives simultaneously. If one drive fails, the other has a complete, current copy, and you can keep working while you replace the failed drive. Rebuilds are simple: the new drive is populated with a straight copy from the surviving one. The tradeoff is capacity — a pair of drives in RAID 1 gives you the usable capacity of one drive, no matter how many terabytes each drive holds.
How RAID 5 works
Three or more drives, striped data, distributed parity. Instead of a full duplicate, RAID 5 calculates a parity value from the data across the other drives and spreads that parity around so no single drive is a bottleneck or single point of failure. This gives you the usable capacity of all drives minus one, which is significantly more efficient than mirroring as you add drives. The cost shows up when a drive fails: rebuilding requires reading every remaining drive in full to recalculate the missing data, which stresses the surviving drives for hours, sometimes over a day on large modern capacities.
RAID 1 vs RAID 5 comparison
| Aspect |
RAID 1 |
RAID 5 |
| Minimum drives |
2 |
3 |
| Usable capacity |
50% of total (1 drive worth) |
Total minus 1 drive |
| Rebuild speed |
Fast, simple copy |
Slower, full parity recalculation |
| Rebuild risk |
Lower, less drive stress |
Higher, especially on large drives |
| Best fit |
Small NAS, boot volumes, simplicity |
Larger arrays prioritizing capacity efficiency |
Choosing between them for a home setup
If your NAS has only two bays, RAID 1 is essentially your only redundancy option and it is a solid one. If you have four or more bays and are choosing between RAID 5 and RAID 10, consider that RAID 10 (mirrored pairs, striped together) gives up some capacity efficiency compared to RAID 5 but rebuilds faster and tolerates certain two-drive failures that would kill a RAID 5 array. For most home users prioritizing safety over squeezing out every gigabyte, that tradeoff is usually worth it. Whichever RAID level you pick, back up anything irreplaceable outside the array — see our best NAS for home guide for how RAID fits into a full storage strategy, and what is a JBOD array for the no-redundancy alternative some users prefer for pure capacity.
FAQ
Can I switch from RAID 5 to RAID 1 without losing data?
Some NAS operating systems support in-place RAID level migration, but it is a risky, hours-long operation. Back up fully before attempting it regardless of what the software claims.
Is RAID 5 dead because of rebuild risk?
Not dead, but its ideal use case has narrowed. It still makes sense for smaller drives, three-bay arrays, or setups with frequent, verified backups reducing the stakes of a rebuild failure.
Does RAID 1 protect against accidental deletion?
No. A deleted file is deleted on both mirrored drives simultaneously. RAID protects against hardware failure only, not human error or malware.
What is the difference between RAID 5 and RAID 6?
RAID 6 adds a second parity block, tolerating two simultaneous drive failures instead of one, at the cost of one additional drive worth of usable capacity.
Where to go next