You hear the word RAID mainly with servers and NAS storage. It sounds technical, but the principle is simple and worth understanding, mostly so you do not expect something from it that it cannot do.

What RAID is

RAID is a way to combine several disks so that they act as one on the outside. It is done for two reasons: for safety (when one disk fails, the data survives) or for speed and capacity (the disks share the work). Some levels do both at once.

The most common levels, explained

  • RAID 1 (mirroring). Two disks holding the same copy of the data. When one fails, the other keeps running and you lose nothing. A simple insurance against a disk failure.
  • RAID 0 (striping). Two disks combined for higher speed and capacity, but with no protection at all. If even one fails, you lose everything. On its own it is a risk, not a safeguard.
  • RAID 5 and 6. Three or more disks that can survive the loss of one (RAID 5) or two disks (RAID 6) without losing data, while saving capacity. A common solution in NAS units and servers.
  • RAID 10. A combination of mirroring and striping, that is speed and safety at once. It needs four disks.

The protective levels usually also allow hot-swap: you pull out the failed disk and replace it with a new one without shutting down, and the array rebuilds itself.

The most important sentence in this article: RAID is not a backup

This is the one to remember. RAID protects against a disk failure, that is against hardware. It does not protect you from what hits all disks at once:

  • a file deleted or overwritten by mistake,
  • ransomware that encrypts everything, including the mirror,
  • fire, theft, a power surge or a failure of the controller itself.

In all these cases the damage is written to every disk in the array equally. That is why RAID and a backup are not the same thing and one does not replace the other.

When you really need RAID

RAID makes sense where continuous availability matters: a NAS that has to run all the time, a company server, camera recordings. Thanks to redundancy, a single disk failure does not bring down the whole system and you have time to replace it.

For an ordinary household it is often wiser to have one reliable disk plus a proper backup than a complex array with no backup.

Planning storage for a company or a NAS at home? Get in touch and we will design a solution that makes sense, including a backup that actually protects you.