HexOS / TrueNAS Pool Planner

Estimate usable ZFS capacity before you build or expand.

Plan RAIDZ, mirror, stripe, and advanced dRAID layouts with a cleaner HexOS-style interface, realistic headroom targets, and mixed-drive behavior that reflects how ZFS actually groups disks inside each VDEV.

Start Planning Advanced dRAID

RAIDZ1 / 2 / 3
Mirror
Stripe
dRAID

The estimate is geometry-based, not byte-perfect. Real ZFS pool capacity will land slightly lower once filesystem overhead and metadata are applied.

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Recommended all-around NAS drive

WD Red Pro 14TB

Excellent middle ground for 4-to-8-bay HexOS builds.

WD Red Pro 14 TB

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Pool Builder

Choose a layout, set how many VDEVs are in the pool, and size the disks inside each VDEV.

Pool layout

VDEVs in pool

Drives per VDEV

Advanced: mixed VDEV widths Let each VDEV use a different drive count. Leave this off for the simpler matching-width builder.

Need dRAID for a large or specialized array? Open the advanced estimator below.

Set all drive sizes

Units

Pool Summary

Capacity is estimated from your VDEV geometry. Larger disks in a mixed VDEV are clipped to the smallest drive in that same VDEV.

                            Estimated Pool Capacity
                            0 TiB
                        

Recommended Max Fill 0 TiB

Raw Disk Capacity 0 TiB

Redundancy Reserved 0 TiB

Lost to Mismatched Sizes 0 TiB

Total Drives 0

Fault Tolerance Waiting for layout selection
Layout Formula Waiting for layout selection
Expansion Note Waiting for layout selection

Enter drive sizes to see how the pool changes when you add more VDEVs or change the redundancy level.

Recommended NAS Drives

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HexOS Storage Terms

The old parity/data-disk language does not map well to ZFS, so the calculator now uses HexOS and TrueNAS terms instead.

Pool vs. VDEV

A pool is the top-level storage space. A VDEV is the building block inside that pool. Total usable pool space is the sum of the usable capacity from every VDEV.

RAIDZ Math

RAIDZ1, RAIDZ2, and RAIDZ3 reserve one, two, or three drives worth of capacity per VDEV for redundancy. Mixed-size VDEVs behave like every disk is the size of the smallest disk in that group.

Plan for Headroom

ZFS performs best with free space available. The calculator shows a recommended 80% max fill so you can plan snapshots, resilvers, and normal growth without painting yourself into a corner.

Advanced calculator: dRAID estimator Not the default. Find it here when you need TrueNAS/OpenZFS dRAID math.

Based on the TrueNAS dRAID primer formula: Capacity = (C - S) × (D / (D + P)) × DS. TrueNAS documents dRAID for very specific use cases, especially very large arrays, and warns that it can be less space-efficient than RAIDZ for general workloads.

dRAID VDEVs in pool

Children / drives per VDEV (C)

Data devices per group (D)

Parity level (P)

Distributed hot spares (S)

Minimum common disk size (DS)

                            Estimated dRAID Pool Capacity
                            0 TiB
                        

Recommended Max Fill 0 TiB

Raw Disk Capacity 0 TiB

Parity + Spare Reservation 0 TiB

Distributed Spares Only 0 TiB

Total Drives 0

dRAID Fault Model Waiting for dRAID inputs
Layout Formula Waiting for dRAID inputs
Expansion Note Waiting for dRAID inputs

Open the panel and enter your layout to estimate dRAID capacity using the documented TrueNAS formula.