RAID 5 is a redundant disk array configuration that requires at least three physical drives. It balances storage efficiency, read performance, and fault tolerance. Unlike mirroring, RAID 5 uses parity bits to reconstruct data if any single drive in the array fails.
How it works
Data is divided into blocks and spread across all disks in the array (striping). Parity information is calculated using the XOR logical operation and distributed across all members of the set instead of being stored on a dedicated parity drive. This prevents the performance bottleneck during write operations common in RAID 4.
Typical use cases include file servers, backup repositories, and systems where read operations dominate. RAID 5 is generally avoided for high-transaction databases due to the "write penalty"—the overhead of reading old data and parity before writing new blocks.
The usable capacity is calculated as (n-1) * capacity, where n is the number of drives. For instance, a four-drive array with 2 TB disks provides 6 TB of usable space. Rebuild time is a critical factor: with high-capacity HDDs, the risk of a second drive failure during reconstruction increases significantly, potentially leading to total data loss.