Hey there, i have installed 4 disks with 18 TB of capacity. 16,37TiB as usable space per disk. 4 x 16,37 = 65,48 TiB minus one disk for parity should come out to 49,11 TiB. My storage tab only showes me a usable cpacity of 43.48 TiB. Somehow 5,63 TiB are missing and I miss them dearly… =) Could a…

Probably due to ZFS overhead. The ZFS Capacity Calculator is a good resource.

Are you sure all your drives are 18TB? 43.48TB is suspiciously close to what you would get with 16TB drives (even one 16TB drive among 18TB can give this result).

Thx for your reply… I am positive that they all are 18TB… [x01] [x02] [x03] I am wondering if the problem is sitting infront of the nas or if it is internal? =)

I recently moved from a Sonology nas to Truenas. I set up truenas (first install nothing imported) with 3x18TB to begin with a couple of days ago and the storage space shown was alright. Then I copied all the data from a single 18TB disk to the Truenas pool. After that was done I expanded the 3x18 p…

[image] chuck: After that was done I expanded the 3x18 pool with the fourth 18TB disk. That solves the mystery, see 24.10 RC2 Raidz expansion caused miscalculated available storage

[image] chuck: After that was done I expanded the 3x18 pool with the fourth 18TB disk Seems like this is the reason for the size discrepancy. In short, you actually have your space, but the reporting is wrong. There is an entire tag on this forum for the issue. You should give it a read. Per…

Thanhk you J_B and swc_phil! Will read this and hope that this will solve my problem… Cheers

Truenas Community Edition RAIDZ1 Pool Size Mystery

TrueNAS General

etorix September 10, 2025, 3:57pm 12

This will only “solve” the issue in that you know why reports are wrong, but there’s no way to fix it other than by destroying the pool.

As pictured here:

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Truenas Community Edition RAIDZ1 Pool Size Mystery

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