Strange arithmetic

[pdenommee]

I am done with my build of an NAS of 6 6TB hard drives in raidZ2. I do not understand the output. The reported size of the empty volume is 31.2 TiB. After writing 908.2 Gb of data to the server, the new reported size of the volume is 20.1 TiB. So writing less the a TiB to the disk did cause the loss of 11.1 TiB. Windows also report "only" 20.1 TiB. The files on the NAS are all .tib from Acronis True Image. This file format is already compress and is no longer compressible.

There is no periodic snapshot task, so snapshots are not using space behind the scene.

 

[nightshade00013]

Looks fine to me. The problem is RaidZ2 = Drives -2, since you use two drives for parity you get the capacity of 4 drives in your case and TB ≠ TiB.

 

[pdenommee]

The infamous TiB vs TB problem, drive manufacturers want the capacity to be as high as possible.