How does zvol use space in zpool?

Question

ZFS

There is a storage on freenas, I create a zvol on it and announce iscsi.
I searched all the documentation ( docs.oracle.com/cd/E19253-01/820-0836 ), but I can't figure out how this zvol uses space in the zpool ?

For example, I have created such a 4 Tb zvol
under the name data / hv-data.

Having written 1 Tb there, I see that it takes 5 TB

how does it work?
what are the values ​​of the fields
AVAIL USED USEDSNAP USEDDS USEDREFRESERV USEDCHILD
?

There are more properties


and descriptions like there are docs.oracle.com/cd/E19253-01/820-0836/gazsd/index.html
but still does not bring clarity.

Answer 1

Dynamically. Of necessity.
You can have 10 zvol for a 1 terabyte zpool.
And that's who the first of these 10 zvol will take this terabyte - that and slippers.

Answer 2

I recommend reading "FreeBSD Mastery: ZFS" by Michael W. Lucas, Allan Jude .
What is explained in detail and clearly.