Guide · ZFS
ZFS RAIDZ Explained
RAIDZ is ZFS's built-in parity RAID. Unlike hardware RAID, it lives inside the filesystem, so ZFS checksums every block and can repair silent corruption during a scrub. There are three levels, defined by how many parity disks each vdev carries.
RAIDZ1, RAIDZ2, RAIDZ3
- RAIDZ1 keeps one parity disk and survives one disk failure. Usable space is roughly (N − 1) × the smallest disk.
- RAIDZ2 keeps two parity disks and survives two failures. Usable space is roughly (N − 2) × the smallest disk. This is the common homelab default.
- RAIDZ3 keeps three parity disks and survives three failures, for wide vdevs where rebuild times are long.
Why "roughly"
ZFS allocates in records and pads stripes to keep them aligned to the pool's ashift. With small records or odd disk counts, real usable space can sit a few percent below the simple (N − parity) estimate. Plan with the estimate, then confirm on the live pool.
Which should you pick?
For most homelab pools of 4 to 8 large drives, RAIDZ2 is the safe choice: it survives a second failure during the long rebuild a large drive needs. RAIDZ1 is reasonable only for small disks or non-critical data. See why single parity is risky with large drives.