Where has my available space gone?

[Tony Self]

I have recently upgraded my 8 disk Z2 main volume from 3TB disks to 8TB disks. However I seem to have lost a huge chunk of available disk space. If you look at my main ZVol it shows available space of 37.5TB, but the main dataset only shows available space of 25.3TB. I seem to have lost over 12TB in overhead of some sort. That's nearly a third of my available space.
On my SSD ZVol the overhead is far less.

Can someone explain what is going on here and how I can recover the space?

Thanks

 

[DrKK]

Is there any chance you set a "quota" on the dataset? That's how it will manifest, if so. Also, "zpool list" should show nothing in the "EXPANDSZ" column, please verify that's the case.

 

[Bidule0hm]

Just to be sure you didn't overlooked something: available is total minus used, so it'll decrease when you fill the pool (which is about one third full, and you say there's a third missing...).

The total (used + available) should remain the same however.

 

[cobrakiller58]

using @Bidule0hm 's calulator it looks about right to me space wise you lose two drives to parity data http://doc.freenas.org/11/storage.html#view-volumes

 

[Ericloewe]

If you look at my main ZVol

That is not a zvol, that is the pool's top-level dataset. A zvol is a dataset that provides block storage instead of a filesystem.

As for "missing" storage, I don't see anything obviously off. You have an estimated capacity of 39 TB, whereas your pool is nominally capable of ~43 TB. Since you get zero compression out of your media, metadata is going to take up a noticeable chunk of those 43 TB.

 

[danb35]

If you look at my main ZVol it shows available space of 37.5TB, but the main dataset only shows available space of 25.3TB.

From the manual:

Note that in this example, there are two datasets named volume1. The first represents the ZFS pool and its Used and Available entries reflect the total size of the pool, including disk parity. The second represents the implicit or root dataset and its Used and Available entries indicate the amount of disk space available for storage.