RAID Usable Storage Calculator
Calculate usable storage capacity for RAID 0, 1, 5, 6 and 10 configurations.
Results
RAID (Redundant Array of Independent Disks) combines multiple drives for performance, redundancy or both. Each RAID level trades usable capacity for fault tolerance differently. RAID 0 uses all capacity but has no redundancy, while RAID 1 mirrors drives and RAID 5/6 use parity. This calculator shows exactly how much usable storage each RAID level provides.
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Frequently asked questions
RAID 5 with 4 drives gives (N-1) x size = 3 x 4 TB = 12 TB usable. One drive's worth of capacity (4 TB) is used for parity, giving 25% overhead.
RAID 5 uses single parity (1 drive overhead, tolerates 1 failure). RAID 6 uses double parity (2 drives overhead, tolerates 2 failures). For 6 x 4 TB drives: RAID 5 = 20 TB usable, RAID 6 = 16 TB usable.
No. RAID 0 stripes data across drives with zero redundancy. If any single drive fails, all data is lost. RAID 0 should only be used for temporary data, scratch disks or caches where speed matters more than reliability.
RAID 10 can tolerate 1 drive failure per mirrored pair. In the best case, half the drives can fail (one from each pair). In the worst case, losing both drives in one pair destroys the array.
RAID 5 is the most popular choice for home NAS with 3-5 drives - it gives a good balance of usable space and protection. For 6+ drives or critical data, RAID 6 adds a second layer of parity protection.