How to know what zfs storage capacity is available

I have a zpool which is closing up on 75% CAP - which I wonder how to interpret from a capacity point of view.

The pool looks like this:

default  8.58T  6.43T  2.14T    75%

But, from experience, I know that my storage starts to behave very “slow” when reaching about 80% CAP.

This leaves alot of space “unusable” ?

Is there a way to allow for use of the full capacity (or at least 90% or so).

AFAIK, you can fill up the pool to 100% but at a certain point, you’ll hit a speed degradation as you noticed. Upstream recommends to keep 10% free space:

With older ZFS versions, it was previously recommended to only fill up to 80%, especially on spinning drives:


Right, thanx for the info!