Notice that /var space isn't showing, however /var is full-fledged dataset, thus it's a filesystem from df's point of view: [root@db1:/etc]# df -h Filesystem Size Used Avail Capacity Mounted on zroot/ROOT/default 126G 1,2G 124G 1% / devfs 1,0K 1,0K 0B 100% /dev zroot/tmp 124G 160K 124G 0% /tmp zroot/usr/home 124G 2,1M 124G 0% /usr/home zroot/usr/ports 126G 1,7G 124G 1% /usr/ports zroot/usr/src 124G 88K 124G 0% /usr/src zroot/var/audit 124G 88K 124G 0% /var/audit zroot/var/crash 124G 88K 124G 0% /var/crash zroot/var/db 125G 136M 124G 0% /var/db zroot/var/db/mysql 362G 238G 124G 66% /var/db/mysql zroot/var/log 124G 692K 124G 0% /var/log zroot/var/mail 124G 332K 124G 0% /var/mail zroot/var/tmp 124G 88K 124G 0% /var/tmp zroot 124G 88K 124G 0% /zroot zroot/public 173G 48G 124G 28% /usr/local/public [root@db1:/etc]# zfs list NAME USED AVAIL REFER MOUNTPOINT zroot 290G 124G 88K /zroot zroot/ROOT 1,18G 124G 88K none zroot/ROOT/default 1,18G 124G 1,18G / zroot/public 48,1G 124G 48,1G /usr/local/public zroot/tmp 160K 124G 160K /tmp zroot/usr 1,73G 124G 88K /usr zroot/usr/home 2,12M 124G 2,12M /usr/home zroot/usr/ports 1,73G 124G 1,73G /usr/ports zroot/usr/src 88K 124G 88K /usr/src zroot/var 239G 124G 88K /var zroot/var/audit 88K 124G 88K /var/audit zroot/var/crash 88K 124G 88K /var/crash zroot/var/db 239G 124G 136M /var/db zroot/var/db/mysql 238G 124G 238G /var/db/mysql zroot/var/log 692K 124G 692K /var/log zroot/var/mail 332K 124G 332K /var/mail zroot/var/tmp 88K 124G 88K /var/tmp
df reports only mounted filesystems. I am certain that your zroot/var is not mounted.
You're right, it is not mounted indeed. But then this merely isn't logical: canmount is set to off by basdinstall, and zroot/var does exist, thus /var in reality appears to be a directory inside zroot/ROOT/default. Concluding: bsdinstall creates the zroot/var dataset, but doesn't mount it and /var is a zroot/ROOT/default directory. Why ?
I guess it's so that there can be a finer control over what goes to /var directory in a boot environment and what goes to shared datasets created as children of zroot/var. Also, the children inherit properties from the parent, so that's also a convenience.