RAID at a glance
| Level | Minimum drives | Usable space | Survives | Best for |
|---|---|---|---|---|
| RAID 0 | 2 | 100% of all drives | No drive failure | Speed and capacity for data you can lose |
| RAID 1 | 2 | 1 drive | 1 drive failure | Most servers with two drives |
| RAID 5 | 3 | All drives minus 1 | 1 drive failure | Balance of space and protection |
| RAID 6 | 4 | All drives minus 2 | 2 drive failures | Large arrays and critical data |
| RAID 10 | 4 | 50% of all drives | 1 drive per mirror | Databases and busy applications |
RAID 0 — striping
Data is split across all drives, so reads and writes are fast and you get the full combined capacity. There is no redundancy: if one drive fails, everything on the array is lost. Use it only for temporary data, caches or anything you can rebuild easily.
RAID 1 — mirroring
Every piece of data is written to two drives at once. If one drive fails, the other keeps working and the server stays online while the failed drive is replaced. You get the capacity of one drive. For a server with two drives, RAID 1 is the safe default.
RAID 5 — striping with parity
Data and parity information are spread across three or more drives. The array survives one failed drive and loses only one drive's worth of space. Writes are slower than RAID 10, and rebuilding a large array after a failure takes time — during which a second failure would be fatal.
RAID 6 — double parity
Like RAID 5 but with two sets of parity across four or more drives, so the array survives two failed drives. It costs two drives of capacity and writes more slowly, but it is the safer choice for large drives and important data.
RAID 10 — mirroring plus striping
Drives are paired into mirrors, and data is striped across the pairs. You get the speed of striping and the protection of mirroring, with fast rebuilds — at the cost of half your total capacity. It needs at least four drives and is the usual choice for busy databases.
RAID is not a backup
Which RAID level should you choose?
- Two drives: RAID 1 for protection (recommended), or RAID 0 only if speed and capacity matter more than the data.
- Three drives: RAID 5.
- Four or more drives: RAID 10 for databases and performance, RAID 6 for maximum protection of large volumes.
Every VeloServers dedicated server comes with two drives, and storage is upgradable. At checkout you can add drives, choose the RAID level your drive count supports, and add backup storage.