Calculate usable capacity of a RAID 5 array accounting for single-disk parity.
RAID 5 distributes parity data equivalent to one disk's capacity across all member disks, so usable capacity is (n − 1) × disk_size. This provides single-disk fault tolerance — any one disk can fail without data loss, but a second simultaneous failure causes total array loss. RAID 5 requires a minimum of 3 disks and offers a good balance between capacity efficiency and redundancy for most workloads.
RAID 5 usable capacity
usable = (n − 1) × disk_size
Storage efficiency
efficiency = (n − 1) / n × 100%
RAID 5 requires at least 3 disks: n − 1 disks worth of usable capacity with 1 disk worth of parity distributed across all members.
RAID 5 only tolerates a single disk failure. If a second disk fails before the array is rebuilt, all data is lost. For dual-disk fault tolerance, use RAID 6 instead.
No. RAID protects against individual disk failure but not against accidental deletion, corruption, ransomware, or site-level disasters — separate backups are still required.