RAID Levels Explained
- RAID combines multiple hard drives into one storage volume on a NAS or server.
- It can protect against some drive failures — it is not a backup.
- Usable space is almost always less than the sum of the drive sizes.
- Prefer the same capacity and series of drives when building a new array.
What is a RAID configuration?
A RAID configuration is the mode your NAS uses to organise the drives. You choose the mode when you create the storage volume (for example in Synology DSM). The mode decides:
- How much space you can use
- How many drives can fail before data is at risk
- How the system behaves when a drive is replaced (rebuild)
Your NAS must be diskless + compatible drives first. RAID is set up in software after the drives are installed.
RAID levels at a glance
| Level | Min drives | Survives | Usable capacity (approx.) | Good for |
|---|---|---|---|---|
| RAID 0 | 2 | 0 failures | Nearly all | Speed only — not for important data |
| RAID 1 | 2 | 1 drive | About half | 2-bay home / small office |
| RAID 5 | 3 | 1 drive | About (n − 1) drives | 4-bay small business |
| RAID 6 | 4 | 2 drives | About (n − 2) drives | Larger business arrays |
| RAID 10 | 4 | 1 per mirror pair | About half | Performance + protection |
| SHR (Synology) | 1–2+ | Depends on setup | Flexible | Most home & SMB Synology users |
n = number of same-size drives.
Each level explained simply
RAID 0 — speed, no safety net
Data is split across drives for performance. If any one drive fails, the volume can be lost. We rarely recommend RAID 0 for real business or family data.
RAID 1 — mirror (simple and safe for 2 bays)
Everything is written to two drives. If one fails, the other still holds a full copy. You only get about half the raw capacity. Ideal for many 2-bay home and small-office setups.
RAID 5 — balance of space and protection
Needs at least 3 drives. Stores data plus parity so the array can survive one drive failure and rebuild when you replace the drive. A common choice for 4-bay NAS used by small teams.
RAID 6 — safer on larger arrays
Needs at least 4 drives. Can survive two drive failures. Uses more space for protection than RAID 5. Useful when drives are large and rebuilds take a long time.
RAID 10 — mirrors + speed
Combines mirroring and striping. Strong protection and good performance, but you typically use about half the total capacity. Needs at least 4 drives.
SHR — Synology Hybrid RAID
Synology’s flexible mode. Often the easiest choice for home and SMB DiskStations, especially if you may expand later or mix sizes carefully. Protection still depends on how many drives you have — and SHR is still not a backup.
Example configurations
| Drives | Typical mode | Rough usable space |
|---|---|---|
| 2 × 4 TB | RAID 1 or SHR | ~4 TB |
| 4 × 4 TB | RAID 5 or SHR | ~12 TB |
| 4 × 4 TB | RAID 6 or RAID 10 | ~8 TB |
| 5 × 8 TB | RAID 5 / SHR | ~32 TB |
| 5 × 8 TB | RAID 6 | ~24 TB |
Exact numbers vary with filesystem overhead and how the NAS reports TB vs TiB.
How to choose your RAID level
- 2-bay home backup → RAID 1 or SHR
- 4-bay office / media → RAID 5 or SHR (RAID 6 if you want extra failure tolerance)
- Many large drives / critical business → RAID 6 or vendor-recommended layout
- Need speed and can give up capacity → RAID 10
- Always keep an independent backup of important data (another NAS, external drive, or cloud)
RAID configuration checklist
- Confirm drive models on the official compatibility list for your NAS
- Install drives, then create the volume in the NAS OS (e.g. Synology DSM)
- Choose RAID/SHR mode before moving critical data
- Note usable capacity after the volume is created
- Set up a real backup job — RAID alone is not enough
Not sure which RAID level fits you?
Tell us your NAS model (or bay count), what you store, and how many users. We will recommend a sensible layout and matching drives.
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