RAID Explained in Plain English: Which Level Protects Your Files Best

RAID sounds intimidating until you realize it's really just a handful of ways to arrange drives — each with an obvious tradeoff.

RAID stands for "Redundant Array of Independent Disks" — a way of combining multiple hard drives so that data is protected, performance is improved, or both, depending on which arrangement (or "level") you choose. Most NAS devices ask you to pick a RAID level during setup, and the right choice depends entirely on what you're trying to protect against.

RAID 0 — speed, no protection

RAID 0 splits data across two or more drives to increase speed, but provides zero redundancy. If any one drive fails, all the data across the entire array is lost — not just the data on that drive. This is worth mentioning mainly so you know to avoid it for anything you care about keeping; it exists for pure performance use cases, not for a home file server or backup.

RAID 1 — mirroring

RAID 1 writes the exact same data to two drives simultaneously. If one drive fails, the other has a complete, up-to-date copy, and the system keeps running while you replace the failed drive. The tradeoff: you only get to use the capacity of one drive, since the second is entirely a mirror of the first. Simple, reliable, and a sensible choice for a basic two-drive home NAS.

RAID 5 — balance of capacity and protection

RAID 5 requires at least three drives and spreads data plus "parity" information (a kind of mathematical recovery data) across all of them. If any single drive fails, the missing data can be rebuilt from the parity information on the remaining drives. You get to use the equivalent of all but one drive's worth of capacity, which is a better ratio than RAID 1 as you add more drives. The tradeoff is that rebuilding after a failed drive takes time and puts real strain on the remaining drives, and RAID 5 only protects against a single drive failure at a time.

RAID 10 — the best of both, at a cost

RAID 10 combines mirroring and striping, requiring at least four drives. It offers both strong protection (it can survive multiple drive failures, as long as they're not both halves of the same mirrored pair) and better performance than RAID 5. The tradeoff is capacity — like RAID 1, you effectively only get to use half of the total drive capacity you install, which makes it a more expensive way to get the same usable storage.

Which one actually makes sense for a home or small-business NAS

For most households: a two-drive NAS in RAID 1 is a sensible, simple starting point — straightforward to understand, easy to recover from a single drive failure, and a proven approach for a first NAS. For a household or small business with more files, a four-or-more-drive NAS in RAID 5 offers a good balance of usable capacity and protection, and is a common choice for a family's or small office's primary shared storage. RAID 10 is worth the extra drive cost specifically when performance under heavy simultaneous use matters — a small business with several people accessing large files at once, for example.

The one thing RAID doesn't do

RAID protects against a drive failing — it does not protect against theft, fire, flood, ransomware, or accidentally deleting the wrong folder. All of those scenarios can wipe out a RAID array just as completely as a single unprotected drive. RAID is the first layer of protection, not the whole plan — a real backup, ideally with a copy stored somewhere else entirely, is still necessary regardless of which RAID level you choose.