RAID (Redundant Array of Independent Disks) combines the drives inside your NAS so they work together — to protect your data if a drive dies, to go faster, or to pool several drives into one big volume. The level you choose decides how much usable space you get and how many drive failures you can survive.
RAID is not a backup. RAID protects against a drive failing. It does not protect against accidental deletion, ransomware, corruption, a power surge, theft, or fire — in all of those it faithfully copies the problem across every disk. Always keep a separate backup too (3 copies, on 2 types of media, 1 kept off-site). Treat RAID as uptime insurance, not your only copy.
RAID 0 — Striping (speed, no safety). Splits data across all drives for fast reads/writes and keeps 100% of capacity, but has zero redundancy — one drive fails and everything is lost. Only for scratch/temporary data. Min 2 drives.
RAID 1 — Mirroring (the simple safe choice). Writes an identical copy to two drives. You get the capacity of one drive (half your raw space) and can lose one drive with no data loss. The standard for 2-bay home NAS. Min 2 drives.
RAID 5 — Striping with single parity (the popular all-rounder). Spreads data plus one drive’s worth of parity across all drives. Usable capacity = all drives minus one; survives one drive failure. The most popular choice for 4-bay-and-up NAS. Note: rebuilding very large drives takes hours and stresses the rest, leaving a window where a second failure would lose the array. Min 3 drives.
RAID 6 — Striping with double parity (safer for big drives). Keeps two drives’ worth of parity: you lose the capacity of two drives but survive two failures at once — including a second failure during a rebuild. Sensible once you’re on large (16 TB+) drives or storing hard-to-replace data. Writes slightly slower than RAID 5. Min 4 drives.
RAID 10 (1+0) — Mirror then stripe (fast and resilient, pricey on space). Pairs drives into mirrors then stripes across them — speed and redundancy, but only half your raw capacity. Survives at least one failure, more if you don’t lose both halves of a pair. Popular for VMs and databases. Min 4 drives.
SHR — Synology Hybrid RAID (beginner-friendly). Synology-only. Manages RAID for you and lets you mix drives of different sizes while using space efficiently. SHR-1 tolerates one drive failure (like RAID 1/5); SHR-2 tolerates two (like RAID 6). Usually the easiest starting point on a Synology unit.
JBOD — Just a Bunch Of Disks (max space, no protection). Concatenates drives into one large volume with no redundancy and no speed benefit; only useful for combining odd-sized drives. Avoid for anything you care about.
Usable capacity & fault tolerance (example: 4 × 8 TB = 32 TB raw)
| RAID level | Min. drives | Usable (4 × 8 TB) | Failures survived | Best for |
|---|
| RAID 0 | 2 | 32 TB (100%) | 0 | Speed only — disposable data |
| RAID 1 | 2 | 8 TB (2-drive set) | 1 | 2-bay home NAS |
| RAID 5 | 3 | 24 TB (n − 1) | 1 | 4-bay+ all-rounder |
| RAID 6 | 4 | 16 TB (n − 2) | 2 | Large drives / important data |
| RAID 10 | 4 | 16 TB (50%) | 1+ (not both of a pair) | Speed + safety (VMs, databases) |
| SHR-1 | 1–2 | 24 TB* | 1 | Beginners, mixed drive sizes |
| SHR-2 | 4 | 16 TB* | 2 | Beginners wanting extra safety |
| JBOD | 1 | 32 TB (100%) | 0 | Max capacity, no protection |
* SHR matches RAID 5/6 capacity with same-size drives; its advantage shows when mixing drive sizes.
Which should I pick? On a 2-bay NAS use RAID 1 (or SHR-1 on Synology). On 4-bay+, RAID 5 / SHR-1 is the sweet spot; step up to RAID 6 / SHR-2 once drives are large or the data is hard to replace. Use RAID 0 or JBOD only for data you can afford to lose. Whichever you choose — keep a real backup as well.
