The rule to remember
RAID improves availability; it does not create an independent backup. Accidental deletion can be mirrored immediately.
Quick comparison
| Level | Minimum | Typical tolerance | Common reason |
|---|---|---|---|
| RAID 1 | 2 | 1 drive | Simple small NAS |
| RAID 5 | 3 | 1 drive | Capacity efficiency |
| RAID 6 | 4 | 2 drives | More rebuild margin |
| RAID 10 | 4, even | Depends on mirror pairs | Performance and faster rebuilds |
Large drives increase rebuild exposure
A rebuild reads the surviving drives for a long time. For irreplaceable data, compare the extra margin of RAID 6 or an independent backup with the capacity you give up.
A safer decision order
- Identify data that cannot be recreated.
- Fund an independent backup first.
- Set acceptable downtime and drive-failure tolerance.
- Then compare usable capacity.
Sources and official tools
Before you buy: Check the compatibility list and calculator published by your NAS, NVR, or drive manufacturer.
Real-world scenario
For family photos, simple RAID 1 plus an external backup may be appropriate. For a four-bay system, compare RAID 5 efficiency with rebuild time, second-failure exposure, and off-device backup cost in the same decision.
Action checklist
- Classify irreplaceable data
- Set acceptable downtime
- Fund an isolated or off-site backup
- Check vendor compatibility and alerts
Frequently asked questions
Does RAID 6 remove the need for backup?
No. It handles two-drive failure but not deletion, ransomware, theft, or fire.
Is RAID 10 always faster?
Performance depends on workload and implementation; check vendor data and your actual use.
Last reviewed: 2026-08-21