Expansion Capacity - Not getting full space

TrueNAS General
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1

I have 6x8TB array that was expanded from 4 disks. The usable capacity is only showing as 20.7TiB. Array is Z2

I have done a rewrite operation on each dataset which reduced the usage by about 5%, however useable capacity didn’t change.

Any ideas? thanks

2

Search for RAID-Zx-expansion tag and read some posts. A lot is explained about the feature and space reporting

3

thanks, I had a look through and saw NAS-131728, which says that this is maybe expected due to the original block size? However there is no mention of what is expected after a rewrite, which I have performed. I think due to it being a relatively new feature.

4

yeah raidz expansion capacity math is kinda cursed still. in my experience usable space after expanding 4->6 in z2 often stays closer to the old “narrowest” stripe layout until a lot more data is rewritten, and even then the gui number can lag what you expect from a fresh 6-wide pool.

rewrite helping used% a bit but not the headline capacity is something ive seen other people report too. probably not you doing it wrong.

if you havent already, zpool list -v and zfs list -o space after the rewrite sometimes show free that the dashboard still under-reports. for a “clean” full-width layout people usually end up saying the only sure path is a new pool + copy, which sucks. not sure if 25.10 changed the reporting yet. shrug

5

It is explained in the discussion. In short: Still a mess!

Rewrite is expected to slightly improve actual available capacity BUT reporting of available capacity is botched anyway—there is no way to fix it other than another major work on OpenZFS.

6

The PR that @etorix linked was accepted, and barring anything unforeseen, may very well make it into ZFS 2.5. Which then makes it into TrueNAS 27, which is General in 2028.

Soon™!

7

We have until November to use “We got X before GTA 6.”

8

thanks for the responses! I guess there is nothing else can be done at this point. I will wait for that version if it does ever come

9

I think the consensus is that this is purely cosmetic, a reporting issue, so does this mean the percentage use is also wrong? Will this update as I get closer to full capacity? thanks