RAID 1

Mirror across drives. Survives N−1 failures. Simplest path to reliable storage in a 2-bay setup.

Min. drives
2
Usable capacity
smallest drive
Fault tolerance
N−1
Performance
Fast reads, normal writes

How it works

Every drive holds an identical copy of the data. Reads can come from any mirror (often parallelised); writes touch every drive. Recovery is trivial: replace failed drive, OS copies the data over.

Formula: min(drives)

RAID 1 — mirror copyDrive 1D1D2D3D4Drive 2 (mirror)D1D2D3D4
Layout diagram

Pros / Cons

Pros

  • Survives up to N−1 drive failures
  • Simple, no parity calculation overhead
  • Fast reads (read from any mirror)
  • Easy recovery — drives are independent
  • Each mirror is a fully readable copy

Cons

  • Half (or less) usable capacity
  • Write speed = single drive
  • Capacity-inefficient for 3+ drives
  • No protection against bit rot without ZFS

When to use

2-bay NAS where reliability matters more than capacity. Boot drives in servers. Critical small datasets that must survive.

When NOT to use

3+ drive setups — RAID 5/6 or RAIDZ give better capacity for similar safety. Bulk storage where capacity matters.

Try it now

Related

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Bottom line: RAID 1 is the simplest, most foolproof RAID. In a 2-bay it's often the right answer. Beyond 2 drives, capacity-efficiency favours RAID 5/6 or RAIDZ.