zfs create -V 8G -b $(getconf PAGESIZE) -o logbias=throughput -o sync=always -o primarycache=metadata -o com.sun:auto-snapshot=false rpool/swap
mkswap -f /dev/zvol/rpool/swap
swapon /dev/zvol/rpool/swap
добавляем в /etc/fstab
/dev/zvol/rpool/swap none swap discard 0 0
mount -av