1 · Choose a RAID level
Single-parity ZFS vdev. Min 2 drives; 3+ typical.
2 · Configure drives
3 · Drive class
3.5" nearline SAS/SATA capacity HDD — indicative figures.
Advanced — read/write mix, URE rate, ZFS tuning
Calculated for planning. We don't publish prices — a 24-year UK reseller, Servnet confirms the exact drives, array and pricing on quote. IOPS, throughput & rebuild are indicative estimates.
What RAIDZ1 is
RAIDZ1 is ZFS’s single-parity vdev: usable capacity is (drives-per-vdev − 1) × drive size per vdev, and each vdev survives one drive failure. Unlike a hardware RAID 5 calculator, this tool models the real ZFS overheads — the ~3.2% slop reservation and the (parity+1)-sector allocation padding that bites at small recordsize.
A key ZFS fact most calculators miss: a RAIDZ vdev delivers roughly the random IOPS of a single drive, so pool IOPS scale with the number of vdevs, not the drive count. Like RAID 5, RAIDZ1 has no redundancy during a resilver, so it is best reserved for smaller vdevs of modest drives — RAIDZ2 is preferred for wide vdevs of large disks.
A single RAIDZ1 vdev of five 8 TB drives gives ~32 TB usable (parity removed). ZFS then holds back ~3.2% slop; padding is negligible at the default 128 KiB recordsize but would grow sharply for small-block zvols — try switching recordsize in the tool to see it.
Advantages
- Capacity-efficient single parity
- ZFS checksums + scrubs catch silent corruption
- Snapshots, compression and self-healing built in
- Models real slop + padding overhead
Trade-offs
- No redundancy during a resilver
- Random IOPS limited to ~one drive per vdev
- Padding overhead grows at small recordsize / wide vdevs
- A second failure in a vdev loses the pool
Best for
- Smaller home / SMB ZFS pools
- Read-heavy and sequential workloads
- Narrow vdevs (3–5 drives) of modest capacity
Consider another level when
- Wide vdevs of large nearline drives (use RAIDZ2)
- Random-IOPS-heavy workloads (use mirrors)
- Mission-critical data without a second copy
RAIDZ1 — common questions
How is RAIDZ1 usable capacity calculated?
Per vdev it is (drives − 1) × drive size, then ZFS reserves ~3.2% slop and rounds allocations up to a multiple of (parity+1) sectors. At the default 128 KiB recordsize that padding is usually negligible, so a 5 × 8 TB RAIDZ1 vdev gives close to 32 TB usable; at small volblocksize (e.g. 8 KiB zvols) padding can cost a lot more.
Does adding drives to a RAIDZ1 vdev increase IOPS?
No. A RAIDZ vdev delivers roughly the random IOPS of a single drive regardless of width — pool IOPS scale with the number of vdevs. For more IOPS, use more (narrower) vdevs or mirrors rather than one wide vdev.
Is RAIDZ1 safe for large drives?
Like RAID 5, RAIDZ1 has no redundancy during a resilver, so a second failure or a bad block on another disk during rebuild can lose the vdev. For wide vdevs of large drives, RAIDZ2 is the safer choice.