ZVols and refreservation in 9.1

[kuruption]

I noticed this during poking around the CLI, and I was just wondering why it seems that 9.1 sets refreservation on any ZVols it creates. It doesn't appear to do this on datasets, so I was just kind of curious to why this is happening.

Here's my Zvol. I'm trying to figure out why it's using 582G when the ZVol was created at 250G...

Code:

# zfs list -r -t all -o space repo2/esxi/disk04
NAME                                    AVAIL  USED  USEDSNAP  USEDDS  USEDREFRESERV  USEDCHILD
repo2/esxi/disk04                        4.03T  582G    6.36G    324G          252G          0
repo2/esxi/disk04@auto-20130809.0400-6m      -  6.36G        -      -              -          -

And then a look at refreservation...

Code:

# zfs get refreservation repo2/esxi/disk04
NAME              PROPERTY        VALUE      SOURCE
repo2/esxi/disk04  refreservation  258G      local

The same on my other ZVols... here's a 200G ZVol

Code:

# zfs get refreservation repo2/esxi/disk03
NAME              PROPERTY        VALUE      SOURCE
repo2/esxi/disk03  refreservation  206G      local