NAS RAID Levels Explained: RAID 0, 1, 5, 6, 10 and RAIDZ
Storage · Updated · First published · By the Hardware Spec Index editors
RAID combines several drives into one volume for capacity, speed, redundancy, or a mix. A NAS uses RAID or a similar scheme so a failed drive does not take the data with it.
Key facts
| RAID 0 | Usable 100%, tolerates 0 failures |
|---|---|
| RAID 1 | Usable 50%, tolerates 1 failure |
| RAID 5 | Usable (n−1)/n, min 3 drives, tolerates 1 |
| RAID 6 | Usable (n−2)/n, min 4 drives, tolerates 2 |
| RAID 10 | Usable 50%, min 4 drives, 1 per mirror |
| RAIDZ2 | Like RAID 6 on ZFS, tolerates 2 |
| Backup rule | 3-2-1 |
Common levels
RAID 0 stripes data with no redundancy. RAID 1 mirrors two drives. RAID 5 spreads single parity across three or more drives and survives one failure; RAID 6 uses double parity across four or more drives and survives two. RAID 10 stripes across mirrored pairs. ZFS offers RAIDZ1, RAIDZ2 and RAIDZ3 with one, two or three parity drives.
Rebuild risk
When a drive fails, the array rebuilds onto a replacement by reading every remaining drive in full. With 16 TB and larger drives this can take more than a day, during which another failure or read error can be fatal for single-parity arrays. Double parity (RAID 6 or RAIDZ2) is recommended for large drives.
RAID is not a backup
RAID protects against drive failure, not against deletion, ransomware, fire or controller faults. Follow the 3-2-1 rule: three copies of data, on two different media, with one copy off site.
Top-ranked matching records
Highest normalized benchmark index among NAS Systems, Hard Drives in our database that match this guide. Rankings are data, not reviews.
| Model | Category | Benchmark | Price |
|---|---|---|---|
| Kestrix NS-5350 Ultra 8-Bay NAS (10GbE, M.2 Cache) | NAS Systems | 7,387 | $2,349 |
| Novexa NS-2889 SE 8-Bay NAS (1GbE, M.2 Cache) | NAS Systems | 5,206 | $1,419 |
| Novexa NS-4655 Ultra 5-Bay NAS (1GbE, M.2 Cache) | NAS Systems | 4,842 | $1,209 |
| Kestrix NS-5502 Plus 4-Bay NAS (1GbE, M.2 Cache) | NAS Systems | 3,835 | $679 |
| Novexa NS-3546 Ultra 4-Bay NAS (2.5GbE) | NAS Systems | 3,554 | $579 |
| Strivon HD-9312 Pro 24TB 7,200 RPM CMR NAS Hard Drive | Hard Drives | 2,997 | $599 |
| Novexa HD-9333 Core 24TB 7,200 RPM CMR NAS Hard Drive | Hard Drives | 2,963 | $599 |
| Mirenta HD-4037 Ti 24TB 7,200 RPM CMR NAS Hard Drive | Hard Drives | 2,954 | $519 |
Frequently asked questions
Which RAID is best for a 4-bay NAS?
RAID 5 maximizes capacity with single-drive protection; RAID 6 or RAID 10 give more safety at lower usable capacity.
Is RAID 5 safe with large drives?
It is risky with very large drives because rebuilds are long. Double parity is safer.
Do I still need backups with RAID?
Yes. RAID does not protect against deletion, corruption or disasters.
Can I mix drive sizes?
Classic RAID uses the smallest drive's capacity for every member; some NAS systems offer flexible schemes that use mixed sizes better.
Should NAS drives be CMR?
Yes, CMR drives rebuild far more reliably than SMR.
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Cite this page: Hardware Spec Index, “NAS RAID Levels Explained: RAID 0, 1, 5, 6, 10 and RAIDZ”, https://vextor7.com/topics/nas-raid (accessed 2026-10-19).