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NAS & RAID Storage Calculator

Calculate usable space, redundancy, and drive overhead for any RAID level — RAID 0, 1, 5, 6, 10, and ZFS RAIDZ1/2/3. Enter drive count and capacity, compare RAID levels side by side.

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All RAID levels compared for your drive count

RAID levelUsable spaceOverheadDrives lost before data lossMin drives

Usable space figures use binary (1 TB = 10243 GB) storage math. RAID 5/RAIDZ1 and RAID 6/RAIDZ2 share the same capacity formula — ZFS RAIDZ uses variable-width parity, which avoids the RAID 5 write-hole vulnerability but gives the same usable-space result. RAID does not replace backups. See the Proxmox Backup Server guide for a 3-2-1 strategy.

How to use this calculator

Select your RAID level, enter how many drives you have and their individual capacity, and the calculator instantly shows usable space, redundancy level, and what happens when a drive fails.

Use the RAID comparison table at the bottom to see all levels side-by-side for your drive count.

Choosing a RAID level

Zero tolerance for data loss at any point — use RAID 6 or ZFS RAIDZ2. Both survive two simultaneous drive failures and are safe during the rebuild window after the first failure.

Best usable space with one-drive redundancy — RAID 5 or ZFS RAIDZ1. Same effective capacity; ZFS version is safer (no write hole).

Simple mirroring for small arrays — RAID 1 (2 drives) or RAID 10 (4+ drives in mirrored pairs). Lower capacity efficiency but simpler failure recovery and better random read performance.

Maximum space, no redundancy — RAID 0 or JBOD. One drive failure loses everything. Only appropriate for scratch storage or content you have elsewhere.

RAID does not replace backups

RAID protects against drive hardware failure. It does not protect against:

  • Accidental file deletion (the deletion propagates across all drives instantly)
  • Ransomware (encrypts data on all drives simultaneously)
  • Controller failure (the RAID controller itself can corrupt data on failure)
  • Fire, theft, or physical disaster

For a complete data protection strategy: RAID for uptime during a drive failure, plus a 3-2-1 backup strategy with at least one off-site copy. The two layers address different failure modes.