Usable Capacity: 12.79 TiB instead of 14.56 TiB (3.64 TiB * 4 drives)

TrueNAS General
1

I have a RAIDZ2 configuration using 6 drives, each with a capacity of 3.64 TiB, I would expect to have a total usable capacity of 14.56 TiB (3.64 TiB * 4 drives).

Here’s my breakdown:

RAIDZ2:
This is a ZFS (Z File System) configuration that provides double parity protection, meaning it can tolerate the failure of two drives simultaneously.

6 Wide:
The number of drives in the RAIDZ2 configuration, with 6 drives in total.

3.64 TiB:
Each drive has a capacity of 3.64 Terabytes (TiB).

Usable Capacity:
In a RAIDZ2 configuration, the usable capacity is calculated by taking the total capacity of the drives and subtracting the capacity used for parity. In this case, with 6 drives, you have 4 drives worth of usable capacity (6-2).
So, 4 drives * 3.64 TiB = 14.56 TiB.

I however only have the usable capacity of 12.79 TiB after running an expand on the datastore.

Any help would be apricated.

2

Go by with the CLI says for space after expansion and not the GUI. This is a know issue, currently. Not sure if it will ever be ‘fixed’ You can search for past posts, probably with RAID-Zx-expansion tag

1 Like
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Thanks for your advice. Yes the GUI is saying 12.79 TiB but shell shows the following:
dwebster@truenas:~$ sudo zpool list
NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
boot-pool 222G 2.78G 219G - - 1% 1% 1.00x ONLINE -
datastore 21.8T 18.2T 3.62T - - 1% 83% 1.00x ONLINE /mnt