Site en Français
Website in english
ZFS calculator
Calculate ZFS Pool & RAIDZ (OpenZFS)
1.Vdev ZFS Configuration
Disks in the vdev (0 disks) :
2. Protection mode RAIDZ / ZFS
3. ZFS-Specific Settings & Performance
Actual Usable Capacity (ZFS Pool)
4. Server TCO & Costs ZFS / TrueNAS
Mastering OpenZFS Capacity & Pool Architecture
Planning an enterprise ZFS deployment requires a deeper understanding than traditional hardware arrays. Whether you are building an all-flash array on TrueNAS SCALE architecting storage for Proxmox VE, or configuring a backup target on Ubuntu Server, our ZFS Calculator accurately predicts your net usable capacity after accounting for parity overhead, metadata reservation, and ZFS Slop Allocation (~3.2%).
Why Compute ZFS Capacity Differently Than Hardware RAID?
OpenZFS manages storage dynamically using Top-Level VDEVs (Virtual Devices) inside a unified <em>zpool</em>. Because data allocation depends on record size, parity width, and alignment, accurate sizing is critical before initializing your pool:
RAIDZ1 VDEV: Single-parity protection that tolerates one drive failure per vdev. Best suited for smaller pools or SSD-based pools where rebuild times are minimal.
RAIDZ2 VDEV:Dual-parity protection capable of surviving two simultaneous drive failures per vdev. Highly recommended when using enterprise HDDs larger than 8 TB to guard against UREs during resilvering.
RAIDZ3 VDEV: Triple-parity layout offering maximum fault tolerance for high-density storage chassis and critical archive workloads.
ZFS Mirroring (vdev pairs): The ZFS equivalent of RAID 10. Delivers maximum random E/S performance and IOPS with faster resilver times, at the cost of 50% raw storage efficiency.
OPS Estimation, Write Amplification, and ARC Cache:
Storage planning isn’t just about Terabytes—it’s about throughput. Our ZFS calculation engine factors in <strong>write amplification penalties, sequential MB/s, and estimated;random IOPS This ensures your pool handles virtual machine disks (zvols) and database workloads without hitting I/O bottlenecks or pool fragmentation degradation.
Why Use a ZFS RAID Calculator for Your Storage Server?
Paragraph: ZFS (Zettabyte File System) has become the gold standard for data integrity on platforms like TrueNAS, Proxmox, and Ubuntu. However, calculating usable capacity after parity overhead (RAID-Z1, RAID-Z2, RAID-Z3) or mirroring can be tricky. Our online tool helps you simulate Vdev configurations and predict available storage space while accounting for “slop space,” swap partitions, and system reserves.
Optimize Your Server Performance with Our Free Tools
Paragraph: Beyond raw capacity, disk performance for HDDs and SSDs is critical for a stable build. We have developed a suite of specialized tools for sysadmins and hardware enthusiasts:
FIO Results Visualizer: Convert complex JSON logs into readable charts to compare IOPS, throughput, and latency.
RAID Rebuild Time Estimator: Calculate how long it will take to resilver your ZFS pool after a drive failure to assess your data loss risk.
PC Bottleneck Calculator: Identify if your CPU or GPU is limiting your hardware performance in gaming or professional workloads.
How much usable space do I get with RAIDZ2?
RAIDZ2 requires at least 4 disks and uses 2 of them for parity. Your usable space is calculated as (N-2) times the smallest disk capacity. Our calculator also subtracts the ZFS overhead for more accuracy.
Is RAIDZ1 safe for large hard drives?
For modern high-capacity drives (8TB+), RAIDZ2 is highly recommended. The “resilver” (rebuild) time for large drives is long, and a second failure during this process would result in total data loss in RAIDZ1.
What is the ZFS SLOP space reservation?
ZFS reserves about 3.2% (1/32) of the pool capacity as “SLOP” space. This prevents the file system from becoming completely locked or extremely slow when it reaches near-full capacity.
Does this calculator work for TrueNAS and Unraid?
Yes! While Unraid uses a different parity system for its main array, it supports ZFS pools. TrueNAS is built entirely on ZFS. Our tool provides accurate estimations for both systems.
What are IOPS in a RAID configuration?
IOPS (Input/Output Operations Per Second) represent the speed of your array. In a RAIDZ configuration, the write IOPS are generally limited to the speed of a single drive in the VDEV, while read IOPS scale with the number of data drives.
OpenZFS Pool Capacity & Performance Sizing
Accurately forecast usable zpool capacity, block size overhead (ashift), parity distribution, and IOPS metrics across OpenZFS VDEV layouts. Built specifically for TrueNAS, Proxmox VE, and enterprise storage architects.
Why Hardware RAID Sizing Fails for OpenZFS
Unlike legacy hardware controllers that present static virtual disks, OpenZFS combines volume management and file system operations into a unified storage pool (zpool). This architecture introduces unique overhead variables that naive storage calculators overlook.
- ZFS Slop Space Reservation OpenZFS reserves roughly 3.2% (1/32th) of total pool capacity as "slop space" to guarantee critical copy-on-write (CoW) operations and snapshot deletions when pools reach high capacity.
- RAIDZ Parity Padding & Ashift Alignment Dynamic block allocation requires padding based on sector size (ashift=12 for 4K sectors). Narrow RAIDZ vdevs combined with small record sizes can cause up to 20-30% parity waste.
- Dataset Swap & Reservation Limits Systems like TrueNAS and Proxmox carve out OS swap partitions (typically 2GB per drive) and zfs reservation margins to prevent pool lockup beyond 80-90% utilization.
Core Calculation Engine Capabilities
Multi-VDEV Pool Simulation
Combine multiple top-level Virtual Devices (VDEVs) within a single zpool to calculate cumulative IOPS and net usable capacity accurately.
Recordsize & Volblocksize Impact
Simulate how varying recordsize (128k default up to 1M for media) or volblocksize (16k/64k for VM block storage) alters effective capacity and amplification.
ZFS Write Amplification & IOPS
Analyze pool random read/write throughput while factoring in ZFS Intent Log (SLOG/ZIL) offload and ARC cache efficiency.
OpenZFS uses Copy-on-Write (CoW). When a zpool exceeds 80% capacity, the file system switches space allocation algorithms from first-fit to best-fit, which drastically increases write latency and pool fragmentation. Always size your pool using our calculator so that your operational dataset stays below 80% of total pool capacity.
Architected for Modern Storage Operators
🖥️ Proxmox VE Hypervisor Admins
Calculate exact ZVOL allocation bounds for guest virtual machine disks, avoiding unexpected out-of-space panics during snapshot rollbacks.
🗄️ TrueNAS SCALE / CORE Systems
Model topology choices between RAIDZ2 arrays for cold storage pools vs mirrored SSD vdevs for high-performance SMB/NFS file shares.