Confused by available space reporting for dataset/volume? (RAID-Z1)

[victorhooi]

I have a HP MicroServer with 4 bays, and I've just installed 4 x 5.0 TB disks in it.

I've set this up with a RAID-Z1 dataset.

For some reason, FreeNAS is showing a volume, datastore2, with another dataset under it, also called datastore2.

However, the parent volume has 18.1 TB capacity, and the child dataset has 12.8 TB capacity.

Any idea what's going on?

 

[Bidule0hm]

That's normal, look at this link for more details ;)

 

[danb35]

I know I've discussed this in more detail in other posts, but in brief, whenever you create a pool (what FreeNAS calls a volume), a dataset is created with it. FreeNAS reports the total capacity for the pool (i.e., the total capacity of all the disks), and the usable capacity for the dataset (after accounting for parity, ZFS overhead, etc.). Your pool has a capacity of 18.1 TiB (not TB), which matches 4 x 5 TB disks. The dataset shows the usable space, which is ~ 13.5 TiB minus ZFS overhead and such.