The default FreeBSD “Guided Root-on-ZFS” installation allocates all the space for “zroot” storage pool. However, if you’d like to have a smaller zroot, you can modify the partitioning script or partition manually.
This article assumes that you’re trying to install FreeBSD using mirrored mode, on disk ada0 and ada1
Option 1: modify partitioning script “zfsboot”
Find a machine running FreeBSD, mount the installation memsitck, and modify /usr/libexec/bsdinstall/zfsboot on memstick
--- usr/libexec/bsdinstall/zfsboot +++ usr/libexec/bsdinstall/zfsboot @@ -943,8 +943,8 @@ # # 4. Add freebsd-zfs partition labeled `zfs#' for zroot # - f_eval_catch $funcname gpart "$GPART_ADD_ALIGN_LABEL" \ - "$align_big" zfs$index freebsd-zfs $disk || + f_eval_catch $funcname gpart "$GPART_ADD_ALIGN_LABEL_WITH_SIZE" \ + "$align_big" zfs$index freebsd-zfs 16g $disk || return $FAILURE f_eval_catch -d $funcname zpool "$ZPOOL_LABELCLEAR_F" \ /dev/$disk$targetpart
Unmount memstick, and and boot from the memstick on the machine that you’d like to install FreeBSD.
Option 2: Open a shell and partition by hand
During the “partitioning – How would you like to partition your disk?” dialogue, select “Shell – Open a shell and partition by hand”
# Destroy existing zroot, not required if it's a new disk with only 0x00. zpool destroy zroot # Force 4K sectors (2^12 == 4096) sysctl vfs.zfs.min_auto_ashift=12 # Cleanup ada0, not required if it's a new disk with only 0x00. # It is okay to ignore errors in this section gpart destroy -F ada0 graid delete ada0 zpool labelclear -f /dev/ada0 gpart create -s gpt ada0 gpart destroy -F ada0 # Partition ada0 gpart create -s gpt ada0 gpart add -a 4k -l gptboot0 -t freebsd-boot -s 512k ada0 gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 ada0 gpart add -a 1m -l swap0 -t freebsd-swap -s 2g ada0 # use your preferred size here zpool labelclear -f /dev/ada0p2 # please ignore error gpart add -a 1m -l zfs0 -t freebsd-zfs -s 16g ada0 # use your preferred size here zpool labelclear -f /dev/ada0p3 # please ignore error # Cleanup ada1, not required if it's a new disk with only 0x00. # It is okay to ignore errors in this section gpart destroy -F ada1 graid delete ada1 zpool labelclear -f /dev/ada1 gpart create -s gpt ada1 gpart destroy -F ada1 # Partition ada1 gpart create -s gpt ada1 gpart add -a 4k -l gptboot1 -t freebsd-boot -s 512k ada1 gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 ada1 gpart add -a 1m -l swap1 -t freebsd-swap -s 2g ada1 # use your preferred size here zpool labelclear -f /dev/ada1p2 # please ignore error gpart add -a 1m -l zfs1 -t freebsd-zfs -s 16g ada1 # use your preferred size here zpool labelclear -f /dev/ada1p3 # please ignore error # fstab :> /tmp/bsdinstall_etc/fstab printf "%s\t\t%s\t%s\t%s\t\t%s\t%s\n" "# Device" Mountpoint FStype Options Dump Pass# >> /tmp/bsdinstall_etc/fstab printf "%s\t\t%s\t%s\t%s\t\t%s\t%s\n" /dev/ada0p2 none swap sw 0 0 >> /tmp/bsdinstall_etc/fstab printf "%s\t\t%s\t%s\t%s\t\t%s\t%s\n" /dev/ada1p2 none swap sw 0 0 >> /tmp/bsdinstall_etc/fstab # Create storage pool and dataset zpool create -o altroot=/mnt -O compress=lz4 -O atime=off -m none -f zroot mirror ada0p3 ada1p3 zfs create -o mountpoint=none zroot/ROOT zfs create -o mountpoint=/ zroot/ROOT/default zfs create -o mountpoint=/tmp -o exec=on -o setuid=off zroot/tmp zfs create -o mountpoint=/usr -o canmount=off zroot/usr zfs create zroot/usr/home zfs create -o setuid=off zroot/usr/ports zfs create zroot/usr/src zfs create -o mountpoint=/var -o canmount=off zroot/var zfs create -o exec=off -o setuid=off zroot/var/audit zfs create -o exec=off -o setuid=off zroot/var/crash zfs create -o exec=off -o setuid=off zroot/var/log zfs create -o atime=on zroot/var/mail zfs create -o setuid=off zroot/var/tmp zfs set mountpoint=/zroot zroot mkdir -p /mnt/tmp chmod 1777 /mnt/tmp mkdir -p /mnt/var/tmp chmod 1777 /mnt/var/tmp zpool set bootfs=zroot/ROOT/default zroot mkdir -p /mnt/boot/zfs zpool set cachefile=/mnt/boot/zfs/zpool.cache zroot zfs set canmount=noauto zroot/ROOT/default echo zfs_enable=\"YES\" >> /tmp/bsdinstall_etc/rc.conf.zfs echo kern.geom.label.disk_ident.enable=\"0\" >> /tmp/bsdinstall_boot/loader.conf.zfs echo kern.geom.label.gptid.enable=\"0\" >> /tmp/bsdinstall_boot/loader.conf.zfs echo vfs.zfs.min_auto_ashift=12 >> /tmp/bsdinstall_etc/sysctl.conf.zfs exit # installation will start
For implementation detail, check /usr/libexec/bsdinstall/zfsboot
or observing the log at /tmp/bsdinstall_log after guided root-on-ZFS installation.