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ZFS dataset hierarchy on a single user machine

# the pool
zpool create -o ashift=12 -O mountpoint=none -O atime=off -O snapdir=visible rpool /dev/mapper/crypt_zfs

# Create filesystems: rootfs, var and home
# rootfs and home has 2 copy of each file as a mirror in single dev.
zfs create -o copies=2 -o compress=lz4 -o mountpoint=/ rpool/rootfs
zfs create -o copies=2 -o compress=lz4 -o mountpoint=/home rpool/home

# var is not a child of rootfs and the zfs daemon will mount it 
# after systemd creates it, leading to a: cannot mount /var, 
# dir already exists error. see link[1]
zfs create -o compress=lz4 -o quota=20G -o mountpoint=legacy rpool/var
# on the second thought, copies=2 makes more sence than  quota
zfs create -o copies=2 -o compress=lz4 -o mountpoint=legacy rpool/var
# /etc/fstab should be this line only:
rpool/var      /var        zfs        defaults    0 0

# var has 2 children with no compression
zfs create -o compress=off -o mountpoint=/var/portage/distfiles
rpool/var/portage_distfiles
zfs create -o compress=off -o mountpoint=/var/portage/packeges
rpool/var/portage_packages

# swap check blocksize with: getconf PAGESIZE, default is 4K
zfs create -V 4G -b 4K rpool/swap
mkswap -f /dev/zvol/rpool/swap
swapon /dev/zvol/rpool/swap

# snapshot of rootfs before sysupdates
# snapshot of home regularly
# reset var to initial (right after bootstrap) snapshot when it's too big
zfs umount -a
zpool set bootfs=rpool/rootfs rpool
zpool export rpool
zpool import -R /mnt/rpool rpool

chroot /mnt/rpool
# install...

TODO: making rootfs readonly and mounting it readwrite only at system updatws.

[1] https://bbs.archlinux.org/viewtopic.php?id=160825