Storage Parameters

Usable Capacity

12 TB

Fault Tolerance

Number of Drives

Capacity per Drive

Drive Type

RAID Level

Array Resilience

Architecture

RAID 5 • Parity

Fault Tolerance

1 Concurrent Failures Allowed

Current Configuration

RAID 5 (Parity)

12 TB Usable

Total RAW: 16 TB

Disk 01DATA

Disk 02DATA

Disk 03DATA

Disk 04PARITY

Total Drives

4 x 4 TB

Efficiency

75% Utilized

Usable: 12 TBWasted to redundancy: 4 TB

Pros & Cons

PRO: Good balance of capacity/speed/safety
PRO: Cost-effective redundancy
CON: Slower writes due to parity calculation
This setup prioritizes redundancy but has associated performance or capacity costs.

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ZFS RAID Calculator

Use the ZFS RAID calculator above to estimate usable capacity for RAID-Z1, Z2, and Z3 arrays. Used by TrueNAS, Proxmox, FreeBSD, and Ubuntu Server.

What Is ZFS RAID-Z?

ZFS (Zettabyte File System) combines the filesystem, volume manager, and RAID layer into one integrated system. This gives it three advantages over traditional RAID: Copy-on-Write eliminates the write hole, variable stripe width eliminates read-modify-write penalties, and checksums on every block provide self-healing data integrity.

RAID-Z1

Single parity · 3+ drives
Survives 1 failure
Capacity: (N-1)×drive

RAID-Z2

Double parity · 4+ drives
Survives 2 failures
Capacity: (N-2)×drive

RAID-Z3

Triple parity · 5+ drives
Survives 3 failures
Capacity: (N-3)×drive

ZFS Write Performance Advantage

ZFS's Copy-on-Write architecture writes a full stripe every time — no read-modify-write cycle needed. Ars Technica benchmarks (2020) showed RAID-Z2 writing 2.5-4× faster than RAID 6 on identical hardware (8× Ironwolf 12TB). For random 4K workloads, ZFS mirrors outperformed RAID 10 by 5-12×. This is why ZFS is the gold standard for data integrity workloads.

ZFS Recommendations

3-5 drives: Use RAID-Z1. Good balance of space and protection for small home servers.

6-12 drives: Use RAID-Z2. Recommended default for most TrueNAS builds. Survives URE during rebuild.

16+ drives: Use RAID-Z3. Triple parity protects during multi-day rebuilds on massive arrays.

IOPS-heavy (VMs, DBs): Use mirrored vdevs instead of RAID-Z. Multiple mirror pairs striped give the best random I/O performance.