Ubuntu USB Stick Day 2 - Using free space to install ZFS
Daniel Nashed – 20 January 2026 20:32:36
Yesterday I have been using /dev/shm to have disk storge for containerd and Docker.
Today I found a way to get some space from the persistent partition /cow and create a ZFS pool.
RUFS can't make this adjustment. But there is a simple tick:
Just create the USB image with as much of persistent storage as possible.
Then use GParted on Linux to make the partition smaller and create another partition.
After that I booted from the USB stick and did all the installation again using ZFS for Docker.
New disk layout
df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 5.8G 5.3G 529M 92% /cdrom
/cow 30G 5.8G 22G 21% /
tmpfs 16G 8.0K 16G 1% /dev/shm
tmpfs 16G 8.0K 16G 1% /tmp
tank 21G 128K 21G 1% /tank
tank/local 23G 1.4G 21G 7% /local
tank/containerd 21G 384K 21G 1% /tank/containerd
tank/docker 21G 3.3M 21G 1% /tank/docker
ZFS Filesystems
zfs list
NAME USED AVAIL REFER MOUNTPOINT
tank 2.81G 20.9G 104K /tank
tank/containerd 272K 20.9G 272K /tank/containerd
tank/docker 1.41G 20.9G 3.18M /tank/docker
tank/local 1.39G 20.9G 1.39G /local
That's pretty cool. But the original setup was a lot faster. Now I am bound to the USB stick performance.
Before I was just using RAM. At runtime we could still put the Domino data disk into tmpfs for testing ...
Installation notes
# Create zpool
wipefs -a /dev/sda3
zpool create -o ashift=12 -o autotrim=on tank /dev/sda3
zfs set compression=lz4 tank
zfs set atime=off tank
zfs set xattr=sa tank
# Create file-systems
zfs create -o mountpoint=/local tank/local
zfs create -o mountpoint=/tank/docker tank/docker
zfs create -o mountpoint=/tank/containerd tank/containerd
# Link storage location for containerd to the new location
ln -s /tank/containerd /var/lib/containerd
# Ensure Docker uses ZFS and the file-system created
mkdir -p /etc/docker
vi /etc/docker/daemon.json
{
"data-root": "/tank/docker",
"storage-driver": "zfs"
}
# Start Docker and containerd
systemctl start containerd
systemctl start docker
systemctl start docker.socket
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