OpenZFS 2.3 is here, with RAID expansion and faster dedup

Coming soon to April's TrueNAS SCALE release, dubbed 'Fangtooth'

The latest version of OpenZFS offers RAID expansion, plus faster data deduplication donated by iXsystems. The code will be available very soon in the beta of TrueNAS SCALE 25.04.

OpenZFS release 2.3.0 is out, and will be in Linux distros that include ZFS, such as Ubuntu, Proxmox, NixOS and Void Linux – and eventually in FreeBSD, too. This release can be built for FreeBSD from 13.3 up to 14.2, and it is compatible with Linux kernel versions up to the latest LTS version 6.12.

The 2.3.0 version lets users expand an existing array by adding additional drives, and ZFS's built-in deduplication feature is now much faster. Advanced applications which do their own caching, such as some databases, can now bypass the ZFS Advanced Read Cache (ARC) with the new Direct IO support.

The RAID-expansion feature has taken a few years to arrive: we talked about it way back in February 2022. However, the OpenZFS team does have a good reason for moving slowly and cautiously: the last new-feature release of OpenZFS was version 2.2.0 in October 2023, which we looked at shortly beforehand. Unfortunately, that release was closely followed by the discovery of a data-corrupting bug. This had been lurking unseen for years, and was followed by fixed versions, both 2.2.2 and 2.1.14.

Since the core selling points of ZFS are its sophistication and its reputation for keeping your data safe, this bug was a serious blow to the project's good name – and confidence. It's therefore understandable that it has moved forwards very slowly and carefully since. We feel it is worth pointing out that the developers haven't been idle: there have been several more releases in both the 2.1.x and 2.2.x series since then, and as of December 2024, they were up to versions 2.1.16 and 2.2.7 respectively.

So, you shouldn't be surprised by the dates on the project pages that describe the headline new features: RAIDZ expansion and Fast Dedup. RAIDZ is the ZFS version of RAID: it lets you amalgamate multiple disks into one larger volume, with redundancy.

The expansion feature lets you add another drive to an existing array, and then enlarge the array to add the extra space. The data is read from the existing drives and then rewritten across all of them including the new ones, so the expansion is not instant by any means – it could take days, and the new space only becomes available when it's complete. However, the array can be used while this is in progress, and it remains fault-tolerant throughout. If it's interrupted, for instance by a reboot, it resumes where it left off, and it can handle if one of the drives fails during the expansion. Expansion can be repeated multiple times.

The main thing that it doesn't support is changing RAIDZ levels. RAIDZ1 is the ZFS flavor of RAID5, meaning it can tolerate the failure of a single drive; RAIDZ2 has dual parity, like RAID 6, with two redundant drives; RAIDZ3 has triple parity. ZFS has let you provision hot spares for many years, but even with RAID expansion, while you can make a RAIDZ1 bigger, you can't turn a RAIDZ1 into a RAIDZ2: you can't add additional parity drives.

Another desirable fresh feature is Fast Dedup. ZFS deduplication isn't new: ZFS has had that for many years – Oracle's documentation page is dated 2010. However, it was relatively slow and made the server work hard. The Reg FOSS desk has two elderly HP Microservers running TrueNAS, each with four-drive RAIDZ1 arrays, and as they're low-end boxes with a mere 8 GB of RAM in each, wiser heads counselled us not to enable dedup; we were told it would make them bog down very badly, possibly for an indefinite period. The new Fast Dedup feature shouldn't impose such a load.

The company behind TrueNAS, iXsystems, developed Fast Dedup and last February donated it to the OpenZFS project. It's been available since March 2024 in the nightly testing releases of TrueNAS SCALE, which is iXsystems's next-generation NAS OS, based on Debian Linux.

For those who prefer to stick to stable versions of their storage software, OpenZFS 2.3 will be included in TrueNAS "Fangtooth" 25.04, which is due in April. Don't expect these features to come to the older FreeBSD-based TrueNAS Core product, though. As we wrote in March 2024, TrueNAS Core 13 is the final FreeBSD version of TrueNAS. The following month, iXsystems told Register sister site Blocks and Files that no users were being "marooned" by the move. This month, iXsystems announced that TrueNAS SCALE 25.04, codenamed "Fangtooth," is designed to unify the CORE and SCALE lines under a common TrueNAS Community Edition (CE).

The main TrueNAS Scale product page extols its ability to run "Apps, Linux Containers, & VMs." This may not commend it to those who just want FreeBSD reliability for their storage boxes and don't care about running Linux Docker containers. (For that matter, as of version 14.2, FreeBSD includes support for running OCI-compatible container images.) There's now a preliminary website for the community-led fork of the FreeBSD version of TrueNAS, although there isn't really anything to see there yet – but it's called zVault. ®