ZFS

Install

On Ubuntu:

sudo apt install zfsutils-linux zfs-initramfs

Memory usage

Calculation

MAX = (RAM SIZE - 1 GB) * 3/4
MIN = MAX / 32

In practice: 62.5 MB ... 2 GB. Average: RAM SIZE / 8 = 512 MB.

Setup

Set the ARC size to a size that make sense on your hardware, edit /etc/modprobe.d/zfs.conf:

options zfs zfs_arc_max=536870912

or

echo "536870912" > /sys/module/zfs/parameters/zfs_arc_max

This is 512M on my 4G Raspberry Pi. 256 M is 268435456.

Statistics

arc_summary -s arc
arc_summary -s archits

Creating pool and filesystem

Enable few features (when e.g. creating a ZFS pool) in order to do some performance increase:

zpool create \
    -o compatibility=openzfs-2.2 \
    -o ashift=12 \
    -o autotrim=off \
    -O compression=lz4 \
    -O acltype=posix \
    -O atime=off \
    -O relatime=off \
    -O xattr=sa \
    -O normalization=formD \
    -O listsnapshots=on \
    -m /media/zfspool \
    zfspool ${DISK}

Compatibility: see /usr/local/share/zfs/compatibility.d/ or /usr/share/zfs/compatibility.d. Good candidates are:

• grub2: for boot pools, when the kernel and initrd is placed on this file system
• openzfs-2.0-linux: ubuntu-20.04 + ZSTD
• openzfs-2.1-linux: ubuntu-22.04 = ubuntu-20.04 + DRAID + ZSTD

Importing with right names

zpool import -d /dev/disk/by-partlabel

zfs create zfspool/zfs1

Starting services with systemd

On newer systems:

systemctl enable zfs-import-cache zfs-import-scan zfs-import.target zfs-mount zfs-share zfs-volume-wait zfs-volumes.target zfs-zed zfs.target
systemctl start zfs-import-cache zfs-import-scan zfs-import.target zfs-mount zfs-share zfs-volume-wait zfs-volumes.target zfs-zed zfs.target

Encryption

Creating a filesystem:

zfs create -o encryption=aes-256-gcm -o keylocation=prompt -o keyformat=passphrase zfspool/encrypted

Loading the key and mounting the filesystem:

zpool import -l zfspool

or manually:

zfs load-key -r zfspool/encrypted
zfs get keystatus zfspool/encrypted
zfs mount zfspool/encrypted

Trim and Timers

sudo systemctl edit fstrim.timer

You might want to add:

[Unit]
Description=Discard unused blocks once a day

[Timer]
OnCalendar=Daily

But it is more important to add the command to trigger trim:

sudo systemctl edit fstrim

By adding:

[Service]
ExecStart=/usr/bin/zpool trim zfspool

Sharing with NFS

Enable NFS share on your ZFS filesystem (service principal for NFS server: nfs/${server}@${REALM}):

zfs set sharenfs="rw=192.168.100.204,rw=rpi4.local" zfspool/shared
zfs set sharenfs="rw=@192.168.100.0/24,sync,sec=krb5:krb5i:krb5p,root_squash,no_subtree_check" zfspool/shared

or

zfs set sharenfs=on zfspool/shared
exportfs -o sync,sec=krb5:krb5i:krb5p,root_squash,no_subtree_check 192.168.100.0/24:/media/zfs/shared

Check if the share has been exported:

exportfs -s
showmount -e