I had a pool of 4 12 TB HDDs in RAIDZ2. Those drives have a real capacity of 10.91 TB after manufacturer rounding, so the total capacity of the pool was around 20 TB. I added a 5th drive of the same size to the pool, and expected it to increase the total capacity to slightly over 30 TB, but it actu…

[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 RC2, I extended my vd…

That thread is extremely long, but seeing at the end that there are no plans to fix this was depressing. I guess I’m just screwed then.

There’s actually a fix in the making, but it could be around 1-2 years until it gets available since it’s not a truenas issue, but a openzfs issue. The fix has to land in openzfs first before it lands in truenas.

Okay - i think even with the under reported capacity i have right now, it’ll be several years till i need another drive. so hopefully the fix is in by then.

it’s only the space reporting thats broken, you have the full capacity, it’s just not displayed correctly.

I’m wondering if zfs rewrite fix this issue?

not completely as far as i followed the issue

Just try ALL the “space reporting” tools available to you. If the turenas web gui doesn’t report correctly, open a terminal and try “df -h /[volume]”. There are probably other tools too. Good luck!

[image] somethingweird: I’m wondering if zfs rewrite fix this issue? No. And it’s worse than some people think. Not the space reporting… but the difference between zfs rewrite and a re-balancing script. zfs rewrite works at the block level. So compression, checksum, and other attributes can…

Adding a drive added less capacity than expected

TrueNAS General

LarsR August 16, 2026, 1:40pm 2

TLDR: There’s a space reporting bug after expansion

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Missing space after adding a drive to raidz1 TrueNAS General RAID-Zx-expansion	6	120	May 4, 2026
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Expansion Capacity - Not getting full space TrueNAS General SCALE , ZFS , RAID-Zx-expansion	8	121	September 5, 2026

Adding a drive added less capacity than expected

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