Glossary / NAS

RAID 5

RAID 5 combines data striping with distributed parity, allowing an array to keep operating after one member drive fails. It needs at least three drives and does not replace a backup.

What RAID 5 means

RAID 5 is a storage arrangement that stripes data across multiple drives and distributes parity information among them. The parity allows the array to reconstruct data if one member drive fails.

A RAID 5 array generally needs at least three drives. Its usable capacity is commonly based on the total capacity of all member drives minus the equivalent of one drive, although the exact result depends on the NAS implementation and the drives used.

Why it matters on NAS products

On a NAS, RAID 5 can provide a balance between usable capacity and protection from a single drive failure. A supported array can remain available while the failed drive is replaced and the data is rebuilt.

The label is a capability indicator, not a quality rating. “RAID 5 supported” does not by itself establish rebuild speed, controller quality, performance, reliability, or the condition of the drives. It also does not mean the NAS can tolerate two failed drives.

RAID 5 is not a backup. It does not protect against accidental deletion, malware, file corruption, theft, or damage to the NAS and its drives.

When RAID 5 is relevant

RAID 5 matters when a buyer wants drive-failure protection and more usable capacity than a mirrored arrangement may provide. It is most relevant to NAS models with enough drive bays to form a supported RAID 5 array.

It may not matter if the NAS has too few bays, if the intended setup uses a different storage layout, or if the buyer needs protection from more than one simultaneous drive failure. In those cases, nearby concepts such as RAID 1, RAID 6, or RAID 10 may describe different trade-offs.

What to check on a NAS product page

Look for:

The number of drive bays and the minimum drive count required for RAID 5
Whether RAID 5 is explicitly listed among the supported storage modes
Any stated drive-capacity, drive-type, or compatibility limits
Whether the specification distinguishes hardware RAID, software RAID, or a vendor-specific storage system
Whether expansion, replacement, migration, and rebuild behavior is documented
Whether the product provides backup or snapshot features separately from RAID

A RAID 5 flag alone leaves important details unknown. Without fuller product documentation, you cannot infer the supported drive sizes, usable capacity, rebuild behavior, or performance.

Nearby concepts

RAID 0 stripes data without parity or mirroring. RAID 1 mirrors data between drives. RAID 6 uses additional parity for protection against two member-drive failures. RAID 10 combines mirroring and striping. NAS is the network-attached storage system that may provide these storage modes.