Rebooted the server.

`zfs list`

NAME            USED  AVAIL  REFER  MOUNTPOINT
store          1.10T  1.58T   160K  /store
store/backups   264G  1.58T   264G  /store/backups
store/homes     136K  1.58T   136K  /store/homes
store/media     862G  1.58T   862G  /store/media

on the client, with 'backups' mounted, `df -h` reveals:

Filesystem                                    Size   Used  Avail Capacity  iused     ifree %iused  Mounted on
user@quattro._afpovertcp._tcp.local/Backups   47Gi   30Gi   18Gi    63%  7801729   4649100   63%   /Volumes/Backups