RAID Levels Explained
RAID 0, RAID 1, RAID 5 — every NAS and server listing throws these numbers around, and picking wrong means either wasted drives or no protection at all. RAID (redundant array of independent disks) is simply a way to combine drives for speed, safety, or both. This guide explains the levels home users actually meet, in plain language, so you can choose with confidence. If you are still deciding on the box itself, start with whether a NAS is worth it.
TL;DR / Quick Fix
Quick fix: for a two-bay home NAS, use RAID 1 — it mirrors data so one dead drive loses nothing. RAID 0 is faster but doubles your risk; RAID 5 needs three or more drives. RAID is not a backup by itself, so keep a separate copy of anything irreplaceable.
Follow these steps
- Learn what RAID actually does. RAID spreads or duplicates data across multiple drives. Some levels make things faster, some survive a dead drive, and the good ones do a bit of both. It is a strategy, not a brand.
- Understand RAID 1: the mirror. With two drives, RAID 1 writes everything to both. One drive can die completely and you lose nothing — you just replace it and the mirror rebuilds. This is the home default for a reason.
- Understand RAID 0: the gamble. RAID 0 stripes data across drives for speed, but if either drive dies, everything is gone. It doubles both speed and risk — fine for scratch files, terrible for anything you care about.
- Understand RAID 5 and 6: the arrays. With three or more drives, RAID 5 survives one dead drive while wasting less space than mirroring. RAID 6 survives two. These suit bigger arrays; most two-bay home units never offer them.
- Know what RAID does not do. RAID protects against drive death only — not accidental deletion, ransomware, fire, or theft. Deleted files vanish from every mirror instantly. That is why a separate backup still matters.
- Rebuild promptly when a drive fails. When the NAS warns of a dead drive, replace it soon. Running on a degraded mirror is running without a net — a second failure before the rebuild finishes means data loss.
What NOT to do
- Do not use RAID 0 for anything irreplaceable. The speed is real; so is the doubled chance of total loss.
- Do not treat RAID as your backup. One ransomware attack or accidental delete wipes every copy at once — keep an off-site backup.
- Do not mix very old and new drives in an array. The weakest drive sets the pace and the failure odds.
- Do not ignore the degraded-array warning. A NAS running on one surviving drive is unprotected until you replace the dead one.
Frequently asked questions
Can I change RAID levels later?
Usually only by rebuilding the array, which wipes it. Some NAS systems allow migration, but plan your level at setup time.
Does RAID make drives faster?
RAID 0 and some higher levels do. RAID 1 mirrors, so reads can be slightly faster but writes are not — you buy it for safety, not speed.
How many drives do I need?
Two for RAID 1, the home sweet spot. RAID 5 needs three minimum. Start with what your NAS bays support.