ZFS reservations for type=volume

I have a zfs block dataset raid-5400-1/esxi-store1 that I share as an iscsi target and that works great.  I have set a reservation
on that block device equal to its size so that is not sparse and thus while I could over provision guests on the provided LUN,
the storage presented as the LUN capacity will always be available.  At least this is what I want to achieve.

What I find strange is that the reservation does not seem to be applied to the ZFS pool 'raid-5400-1'.  Do you really need
to set your maximum reservation at the pool level, and then apply reservations to all datasets on that volume?  And if so
I would assume you could never set reservations for datasets totaling more than what was reserved for the pool 'raid-5400-1'.

I could build out a test environment and figure out constraints but I'd really like to know the "how it is supposed to work"
not the "how I find it to work".

Thanks in advance.

FreeBSD 14.0-CURRENT #4 main-n253875-8e72f458c6d:

(this is a raidz2 pool - not my draid pool)


root@draid:/usr/src/contrib/bearssl # zfs list -o name,type,used,avail,ratio,compression,reservation,refreservation,volsize raid-5400-1
NAME         TYPE   USED  AVAIL  RATIO  COMPRESS        RESERV  REFRESERV  VOLSIZE
raid-5400-1  filesystem  18.0T  2.08T  1.36x  on                none       none        -               <- no reservation @pool
root@draid:/usr/src/contrib/bearssl #

root@draid:/usr/src/contrib/bearssl # zfs list -o name,type,used,avail,ratio,compression,reservation,refreservation,volsize raid-5400-1/esxi-store1
NAME                     TYPE   USED  AVAIL  RATIO  COMPRESS        RESERV  REFRESERV  VOLSIZE
raid-5400-1/esxi-store1  volume  16.9T  18.5T  1.78x  zstd             15.6T      16.9T    15.6T        <- reservation @dataset

root@draid:/usr/src/contrib/bearssl # zpool list
NAME          SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
ccache       9.50G  9.10G   406M        -         -    88%    95%  1.00x    ONLINE  -
raid-5400-1  24.6T  1.52T  23.1T        -         -     2%     6%  1.00x    ONLINE  -                     <- Free does not reflect reservation @pool
tank         18.5T   605G  17.9T        -         -     0%     3%  1.00x    ONLINE  -
zfsroot       103G  33.3G  69.7G        -         -    31%    32%  1.00x    ONLINE  -
root@draid:/usr/src/contrib/bearssl #




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