Hi everyone, I’ve encountered a massive, unexplained loss of available space immediately after expanding a RAIDZ2 vdev from 4 to 5 disks. The physical space allocated (ALLOC) is now almost exactly double the logical data size (USED), and I’ve worked through and ruled out all of the usual culprits. …

Did you read through this post? [image] 24.10 RC2 Raidz expansion caused miscalculated available storage TrueNAS General I have a server with 6x18tb (16.37TiB) drives in RAIDz2, and due to hardware limitations, needed to start with 4 drives and expand later. Using 24.10 R…

[image] LarsR: here’s a bug with space reporting Hey LarsR, Thanks for the quick response. Now I am going through the post. To clarify, is this bug related to ZFS? Additionally, is this a reporting bug, or should I avoid VDEV expansion altogether until the fix is available? That is, the p…

As far as i can remember it’s a consequence of how raidz expansion currently works but i don’t know the exact technical details. I don’t plan on using raidz expansion anytime soon so i just scimmed over the explanations… And as far as i can remember the zfs devs work on an improvement on the raidz e…

[image] LarsR: s far as i can remember it’s a consequence of how raidz expansion currently works but i don’t know the exact technical details. I don’t plan on using raidz expansion anytime soon so i just scimmed over the explanations… And as far as i can remember the zfs devs work on an improvem…

What happens if you use zfs rewrite? Does that “fix” the issue?

[image] NugentS: What happens if you use zfs rewrite? It allows you to recover some capacity by rewriting the data with the new parity-to-data ratio, but it will keep reporting the wrong used/free space.

[image] Reck_Vinci: Basically, for all practical purposes, VDEV expansion is broken. I now have to create zpool from scratch! Extra space is available, so “for practical purposes”, raidz expansion does (about) what is is intended to; only reporting is borked. Do not expect a fix. With “only…

[image] etorix: Extra space is available, so “for practical purposes”, raidz expansion does (about) what is is intended to; only reporting is borked. Do not expect a fix. I only just added a fifth 10TB drive to my Z2 vdev and noticed that I was shortchanged about 5TB in the process. What I di…

RAIDZ2 Expansion: Unexplained 10TB Space Loss & 2x Overhead

TrueNAS General

LarsR September 24, 2025, 7:57pm 2

Did you read through this post?

TLDR:
There’s a bug with space reporting

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RAIDZ2 Expansion: Unexplained 10TB Space Loss & 2x Overhead

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