Volume and Dataset show very different Used and Available storage

[esamett]

I have two Volumes (Tank1 and Tank2) and I want to understand how many TiB I have used and available. As shown in the attached image, Volume: Tank1 has only one Dataset: video-server. Except for FreeNAS overhead I expect the Used and Available numbers to be close but they are not: Used: 12.7 vs. 15.8 Tib, Available: 18.3 vs. 12.4 TiB. Reporting->Datasets shows the lower numbers - 15.8 and 12.4. tank2 is a bit more complex and the backup datasets have quotas to keep Windows in line. I have deleted all Snapshots and emptied all .recycle bins.

Please excuse this semi-repetitive question. I would appreciate any light that can be shined upon this confusion.

 

[Bidule0hm]

The root dataset sizes includes parity (and maybe the checksums too), the sub-dataset(s) sizes don't :)

 

[esamett]

I have lots of files. Is the differential I am seeing reasonable?

 

[Bidule0hm]

The number of files doesn't change anything.

The difference depends on the type of the RAID chosen.

 

[esamett]

Ah. I have Z3 volumes with 11 drives. tank1 has approx 11x4=44TB in total data and 8x4=32TB storage. Adding the Used and Available numbers I get 40 and 28.2 which is much closer.

I see you have 16 drives in Z3 configuration. Are you using multiple vdev or is that one huge volume? (I dread disk upgrade time)

 

[Bidule0hm]

Yeah, the remaining difference is due to the difference between TB and TiB (about 9%).

I have only 8 drives but I think it wouldn't bother me to have a 16 drives with RAID-Z3 (but 16 drives in the same vdev would be my limit) even if I would prefer to keep this number at 12 or less.

 

[esamett]

sixteen seems alot. I have 2 x 11 disk volumes. safer than all together, either with one or two vdev (see calculator at servethehome.com) If only one vdev all need to be replaced to increase storage capacity during upgrade.

 

[Bidule0hm]

Yes, I was talking about home usage, for enterprise storage I wouldn't use so many drives in one vdev.