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<h1 id="zfs"><a class="header" href="#zfs">zfs</a></h1>
<p>Pools are managed with the <a href="https://openzfs.github.io/openzfs-docs/man/8/zpool.8.html"><code>zpool(8)</code></a> command and have the
following hierarchy:</p>
<ul>
<li><code>pool</code>: consists of one or more virtual devices (<code>vdev</code>)</li>
<li><code>vdev</code>: consists of one or more physical devices (<code>dev</code>) and come in
different kinds such as <a href="https://openzfs.github.io/openzfs-docs/man/7/zpoolconcepts.7.html#Virtual_Devices_(vdevs)"><code>disk</code>, <code>mirror</code>, <code>raidzX</code>, ...</a>
<ul>
<li><code>disk</code>: single physical disk (<code>vdev == dev</code>)</li>
<li><code>mirror</code>: data is identically replicated on all <code>devs</code> (requires at least 2
physical devices).</li>
</ul>
</li>
</ul>
<p>Data stored in a pool is distributed and stored across all <code>vdevs</code> by zfs.
Therefore a total failure of a single <code>vdev</code> can lead to total loss of a pool.</p>
<p>A <code>dataset</code> is a logical volume which can be created on top of a <code>pool</code>. Each
<code>dataset</code> can be configured with its own set of <code>properties</code> like
<a href="https://openzfs.github.io/openzfs-docs/man/7/zfsprops.7.html"><code>encryption</code>, <code>quota</code>, ...</a>.
Datasets are managed with the <a href="https://openzfs.github.io/openzfs-docs/man/8/zfs.8.html"><code>zfs(8)</code></a> command.</p>
<h2 id="zfs-pool-management"><a class="header" href="#zfs-pool-management">zfs pool management</a></h2>
<p>Pools are by default mounted at <code>/<POOL></code>.</p>
<h3 id="create-modify-and-destroy-zfs-pools"><a class="header" href="#create-modify-and-destroy-zfs-pools">Create, modify and destroy zfs pools</a></h3>
<pre><code class="language-bash"># Create a pool MOOSE with a two mirror vdevs.
zpool create moose mirror <dev1> <dev2> mirror <dev3> <dev4>..
# Add new raidz1 vdev to a pool.
zpool add moose raidz1 <devA> <devB> <devC>..
# Remove a vdev from a pool.
zpool remove moose <vdevX>
# Destroy a pool.
zpool destroy moose
</code></pre>
<blockquote>
<p>For stable device names in small home setups it is recommended to use names
from <a href="https://openzfs.github.io/openzfs-docs/Project%20and%20Community/FAQ.html#selecting-dev-names-when-creating-a-pool-linux"><code>/dev/disk/by-id</code></a>.</p>
</blockquote>
<h3 id="inspect-zfs-pools"><a class="header" href="#inspect-zfs-pools">Inspect zfs pools</a></h3>
<pre><code class="language-bash"># Show status of all pools or a single one.
zpool status [<pool>]
# Show information / statistics about pools or single one.
zpool list [<pool>]
# Show statistics for all devices.
zpool list -v
# Show command history for pools.
zpool history
</code></pre>
<h3 id="modify-vdevs"><a class="header" href="#modify-vdevs">Modify <code>vdevs</code></a></h3>
<pre><code class="language-bash"># vdev MIRROR-0 with two devs.
zpool status
NAME STATE READ WRITE CKSUM
moose ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
virtio-200 ONLINE 0 0 0
virtio-300 ONLINE 0 0 0
# Attach new device to an existing vdev.
zpool attach moose virtio-200 virtio-400
# vdev MIRROR-0 with three devs.
zpool status
NAME STATE READ WRITE CKSUM
moose ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
virtio-200 ONLINE 0 0 0
virtio-300 ONLINE 0 0 0
virtio-400 ONLINE 0 0 0
# Detach device from vdev.
zpool detach moose virtio-200
</code></pre>
<h3 id="replace-faulty-disk"><a class="header" href="#replace-faulty-disk">Replace faulty disk</a></h3>
<pre><code class="language-bash"># MIRROR-0 is degraded as one disk failed, but still intact.
zpool status
NAME STATE READ WRITE CKSUM
moose DEGRADED 0 0 0
mirror-0 DEGRADED 0 0 0
virtio-200 UNAVAIL 0 0 0 invalid label
virtio-300 ONLINE 0 0 0
# Replace faulty disk, in mirror.
# No data is lost since mirror still has one good disk.
zpool replace moose virtio-200 virtio-400
# MIRROR-0 back in ONLINE (good) state.
zpool status
NAME STATE READ WRITE CKSUM
moose ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
virtio-400 ONLINE 0 0 0
virtio-300 ONLINE 0 0 0
</code></pre>
<h3 id="import-or-export-zfs-pools"><a class="header" href="#import-or-export-zfs-pools">Import or export zfs pools</a></h3>
<p>When moving pools between hosts, the pool must be <code>exported</code> on the currently
active host and <code>imported</code> on the new host.</p>
<pre><code class="language-bash"># Export a pool called MOOSE.
zpool export moose
# If datasets are busy, use lsof to check which processes keep it busy.
# lsof <mntpoint>
# List pools that can be imported using BY-ID deivce names (for example).
zpool import -d /dev/disk/by-id
# Import pool MOOSE using BY-ID device names (for example).
zpool import -d /dev/disk/by-id moose
</code></pre>
<blockquote>
<p>Device names used by an existing pool can be changed by <a href="https://openzfs.github.io/openzfs-docs/Project%20and%20Community/FAQ.html#changing-dev-names-on-an-existing-pool">exporting and
importing</a> a pool again.</p>
</blockquote>
<h2 id="zfs-dataset-management"><a class="header" href="#zfs-dataset-management">zfs dataset management</a></h2>
<p>Datasets are by default mounted at <code>/<POOL>/<DATASET></code>.</p>
<h3 id="create-and-destroy-zfs-datasets"><a class="header" href="#create-and-destroy-zfs-datasets">Create and destroy zfs datasets</a></h3>
<pre><code class="language-bash"># Create dataset FOO on pool MOOSE.
zfs create moose/foo
# Destroy dataset.
zfs destroy moose/foo
</code></pre>
<h3 id="list-all-zfs-datasets"><a class="header" href="#list-all-zfs-datasets">List all zfs datasets</a></h3>
<pre><code class="language-bash"># List all zfs datasets.
zfs list
</code></pre>
<h3 id="mount-zfs-datasets"><a class="header" href="#mount-zfs-datasets">Mount zfs datasets</a></h3>
<pre><code class="language-bash"># List currently mounted datasets.
zfs mount
# Mount dataset.
zfs mount moose/foo
# Unmount dataset.
zfs unmount moose/foo
</code></pre>
<h3 id="encrypted-datasets"><a class="header" href="#encrypted-datasets">Encrypted datasets</a></h3>
<p>Encryption is a readonly property, can only be set when creating a dataset.</p>
<pre><code class="language-bash"># Create encrypted dataset FOO on pool MOOSE.
zfs create -o encryption=on -o keyformat=passphrase moose/foo
# Mount encrypte dataset and load encryption key (if not loaded).
zfs mount -l moose/foo
# -l is equivalent to first loading the key via zfs load-key moose/foo.
# Unmount dataset and unload encryption key (unload is optional).
zfs umount -u moose/foo
</code></pre>
<h3 id="manage-zfs-encryption-keys"><a class="header" href="#manage-zfs-encryption-keys">Manage zfs encryption keys</a></h3>
<pre><code class="language-bash"># Preload encryption key for dataset.
zfs load-key moose/foo
# Preload encryption key for all datasets.
zfs load-key -a
# Change encryption key for dataset.
zfs change-key moose/foo
# Unload encryption key for dataset.
zfs unload-key moose/foo
</code></pre>
<h3 id="manage-dataset-properties"><a class="header" href="#manage-dataset-properties">Manage dataset properties</a></h3>
<pre><code class="language-bash"># Get all properties for dataset.
zfs get quota moose/foo
# Get single property for dataset.
zfs get all moose/foo
# Get single property for all datasets.
zfs get quota
# Set property on dataset.
zfs set quota=10G moose/foo
</code></pre>
<h3 id="snapshots"><a class="header" href="#snapshots">Snapshots</a></h3>
<pre><code class="language-bash"># Create snapshot called V2 for dataset moose/foo.
zfs snapshot moose/foo@v2
# List all snapshots.
zfs list -t snapshot
# Make .zfs direcotry visible in the root of the dataset.
zfs set snapdir=visible moose/foo
# Browse available snapshots in visible .zfs direcotry (readonly).
ls /moose/foo/.zfs/snapshot
v1/ v2/
# Create a new dataset based on the V1 snapshot
zfs clone moose/foo@v1 moose/foov1
# Destroy snapshot.
zfs destroy moose/foo@v1
</code></pre>
<h3 id="access-control-list"><a class="header" href="#access-control-list">Access control list</a></h3>
<p>Focus on <a href="./acl.html">posix acl</a>.</p>
<pre><code class="language-bash"># Set the ACL type for the FOO dataset to POSIXACL.
zfs set acltype=posixacl moose/foo
# Get the ACL type of a given dataset.
zfs get acltype moose/foo
</code></pre>
<blockquote>
<p>For performance reasons it is recommended to also set <code>zfs set xattr=sa moose/foo</code> [<a href="https://github.com/openzfs/zfs/issues/170#issuecomment-27348094">ref</a>].</p>
</blockquote>
<h2 id="example-zfs-pool-import-during-startup-systemd"><a class="header" href="#example-zfs-pool-import-during-startup-systemd">Example: zfs pool import during startup (<code>systemd</code>)</a></h2>
<p>The default zpool cache file is <code>/etc/zfs/zpool.cache</code>. When pools are imported
the cache is updated.</p>
<p>Enable the following targets / services to automatically import pools from the
cache.</p>
<pre><code class="language-bash">systemctl list-dependencies
...
└─zfs.target
└─zfs-import.target
└─zfs-import-cache.service
</code></pre>
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