Introduced in OpenZFS version 2.1.0 and initially supported in TrueNAS 23.10 (Cobia), declustered RAID (dRAID) is an alternate method for creating OpenZFS data virtual devices (vdevs).

Intended for storage arrays with numerous attached disks (>100), the primary benefit of a dRAID vdev layout is to reduce resilver times. It does this by building the dRAID vdev from multiple internal raid groups that have their own data and parity devices, using precomputed permutation maps for the rebuild IO, and using a fixed stripe width that fills storage capacity with zeroes when necessary.

The ZIL and SLOG are two frequently misunderstood concepts in ZFS.

ZFS is taking extensive measures to safeguard your data and it should be no surprise that these two terms represent key data safeguards. What is not obvious, however, is that they only come into play under very specific circumstances.

The first thing to understand is that ZFS behaves like any other file system with regard to asynchronous and synchronous writes.

Determine the usable capacity and other metrics of a ZFS storage pool and compare layouts including stripe, mirror, RAIDZ1, RAIDZ2, RAIDZ3, and dRAID.

Click on the section titles to expand/collapse and view calculated data. Hovering over a table cell loads the relevant data into the Calculation Values section below. You can click table cells to freeze or unfreeze those values.

Visualize and compare different RAID layouts and settings including stripe, mirror, RAIDZ1, RAIDZ2, RAIDZ3, and dRAID.

RAIDZ extension allows TrueNAS users to add disks one at a time to an existing RAIDZ VDEV, incrementally expanding capacity. Use this calculator to estimate the storage capacity efficiency of a ZFS RAIDZ VDEV after incremental extension.

Existing data blocks retain their original data-to-parity ratio and block width, but are spread across the larger set of disks. New data blocks adopt the new data-to-parity ratio and width, or overhead. Because of this overhead, an extended RAIDZ VDEV can report a lower total capacity than a newly created VDEV with the same number of disks.