RAID 5 and RAID 6 are two of the most common RAID levels for NAS systems and servers. Both provide redundancy, but they differ in usable capacity, write performance, and fault tolerance. This guide explains the differences in a simple way so you can choose the right one for your needs.
This is the biggest difference between the two. RAID 6 sacrifices more usable space, but it gives you an extra layer of protection.
| Category | RAID 5 | RAID 6 |
|---|---|---|
| Fault tolerance | Up to 1 failed disk | Up to 2 failed disks |
| Usable capacity | Higher | Lower |
| Write performance | Usually better | Usually slightly slower |
| Best for | Home NAS, capacity efficiency | Critical data, safer long-term storage |
Example with four 8TB disks:
If you want a more detailed explanation, see RAID Capacity Calculation Guide.
RAID 5 can handle one disk failure, but if another disk fails during the rebuild process, the entire array may be lost.
This becomes more important with larger hard drives. As drive capacity increases, rebuild time often becomes longer, and the array stays in a more vulnerable state for longer.
During rebuild, the remaining disks are under heavy load. That is one reason why RAID 6 is often recommended for large drives and important data.
RAID 5 usually has slightly better write performance because it uses single parity. RAID 6 uses double parity, which improves safety but can reduce write speed somewhat.
For many home NAS users, the difference may not be huge in daily use, but in business or high-write environments it can matter more.
The easiest way to understand the capacity difference is to calculate it with your own disk count and disk size.