RAID Calculator
ZFS RAIDZ1
ZFS RAIDZ1
ZFS single parity. Same risk profile as RAID 5 but with checksums, snapshots, and used-block resilver.
How it works
Functionally similar to RAID 5: data and parity stripes across drives. ZFS adds per-block checksums (detects bit rot), copy-on-write (no write hole), snapshots, and used-block resilver — rebuilds only re-create actually-used data, not entire drives. The URE-during-rebuild concern remains: a single uncorrectable read on a surviving drive can leave data lost.
Formula: (N − 1) × min(drives)
Pros / Cons
Pros
- Block-level checksums detect bit rot
- Used-block resilver — only rebuilds actual data
- Native snapshots, replication, compression
- Strong data integrity guarantees
- Free / open source / battle-tested
Cons
- Same URE-during-rebuild concern as RAID 5
- Avoid with drives ≥ 12 TB
- ZFS learning curve
- RAM-hungry (ECC recommended)
- vdev expansion is awkward
When to use
ZFS pools with 3-4 small drives where capacity matters. Test labs, single-vdev secondary pools, backup targets.
When NOT to use
Drives ≥ 12 TB — RAIDZ2 is strongly preferred. Large pools (8+ drives) — too much URE exposure.
Rebuild math example
4 × 8 TB RAIDZ1 at 80% fill: resilver reads (4-1) × 8 × 0.8 = ~19 TB at 70 MB/s ≈ 25 hours. URE risk during resilver remains as in RAID 5; ZFS does NOT magically protect against URE during rebuild.