Btrfs: Difference between revisions

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=== Snapshots ===

Taking a read-only (<code>-r</code>) snapshot called <code>~~nixos_snapshot_202302~~</code> of the subvolume mounted at <code>/</code>

A snapshot in btrfs is simply a subvolume that shares its data (and metadata) with some other subvolume, using btrfs's COW capabilities.

Because of that, there is no special location for snapshots - you need to decide where you want to store them for yourself. It can be a simple directory inside root subvolume, or a directory inside a dedicated "snapshots" subvolume.

For this example we are going to store snapshots in a simple directory <code>/snapshots</code>, that has to be created beforehand with <code>sudo mkdir /snapshots</code>

Taking a read-only (<code>-r</code>) snapshot called <code>home_snapshot_202302</code> of the subvolume mounted at <code>/home</code>

btrfs subvolume snapshot -r /home /snapshots/home_snapshot_202302

</syntaxhighlight>

You can also snapshot the root subvolume. But keep in mind, that nested subvolumes are '''not''' part of a snapshot. So if you have subvolumes <code>/nix /home</code>, taking snapshot of <code>/</code> will not include them.

btrfs subvolume snapshot -r / /~~mnt~~/@nixos_snapshot_202302

btrfs subvolume snapshot -r / /snapshots/nixos_snapshot_202302

</syntaxhighlight>

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btrfs property set -ts /~~mnt~~/~~@nixos_snapshot_202302~~ ro false

btrfs property set -ts /snapshots/home_snapshot_202302 ro false

</syntaxhighlight>

However, changing read-only property of a snapshot in-place may [//lore.kernel.org/linux-btrfs/06e92a0b-e71b-eb21-edb5-9d2a5513b718@gmail.com/ causes issues] with any future incremental send/receive.

Instead, a read-only snapshot itself (being a simple subvolume) can be snapshoted again as a read-write snapshot like this:

btrfs subvolume snapshot /snapshots/home_snapshot_202302 /snapshots/home_snapshot_202302_rw

</syntaxhighlight>

~~List snapshots for~~ <code>/</code>

Or it can be restored directly to <code>/home</code> straight away like this:

{{warning|1=this will delete current <code>/home</code> and restore the snapshot! <code>/home</code> must be unmounted for this operation}}

~~sudo~~ btrfs subvolume ~~list~~ /

btrfs subvolume delete /home

btrfs subvolume snapshot /snapshots/home_snapshot_202302 /home

</syntaxhighlight>

After this you can mount <code>/home</code> again.

=== Transfer snapshot ===

Sending the snapshot <code>/~~mnt~~/@nixos_snapshot_202302</code> compressed to a remote host via ssh at <code>root@192.168.178.110</code> and saving it to a subvolume mounted or directory at <code>/mnt/nixos</code>

Sending the snapshot <code>/snapshots/nixos_snapshot_202302</code> compressed to a remote host via ssh at <code>root@192.168.178.110</code> and saving it to a subvolume mounted or directory at <code>/mnt/nixos</code>

sudo btrfs send /~~mnt~~/@nixos_snapshot_202302 | zstd | ssh root@192.168.178.110 'zstd -d | btrfs receive /mnt/nixos'

sudo btrfs send /snapshots/nixos_snapshot_202302 | zstd | ssh root@192.168.178.110 'zstd -d | btrfs receive /mnt/nixos'

</syntaxhighlight>

[[Category: Configuration]]

[[Category:Filesystem]]

@@ Line 97: / Line 97: @@
 === Snapshots ===
-Taking a read-only (<code>-r</code>) snapshot called <code>nixos_snapshot_202302</code> of the subvolume mounted at <code>/</code>
+A snapshot in btrfs is simply a subvolume that shares its data (and metadata) with some other subvolume, using btrfs's COW capabilities.
+Because of that, there is no special location for snapshots - you need to decide where you want to store them for yourself. It can be a simple directory inside root subvolume, or a directory inside a dedicated "snapshots" subvolume.
+For this example we are going to store snapshots in a simple directory <code>/snapshots</code>, that has to be created beforehand with <code>sudo mkdir /snapshots</code>
+Taking a read-only (<code>-r</code>) snapshot called <code>home_snapshot_202302</code> of the subvolume mounted at <code>/home</code>
+<syntaxhighlight lang="bash">
+btrfs subvolume snapshot -r /home /snapshots/home_snapshot_202302
+</syntaxhighlight>
+You can also snapshot the root subvolume. But keep in mind, that nested subvolumes are '''not''' part of a snapshot. So if you have subvolumes <code>/nix /home</code>, taking snapshot of <code>/</code> will not include them.
 <syntaxhighlight lang="bash">
-btrfs subvolume snapshot -r / /mnt/@nixos_snapshot_202302
+btrfs subvolume snapshot -r / /snapshots/nixos_snapshot_202302
 </syntaxhighlight>
@@ Line 106: / Line 118: @@
 <syntaxhighlight lang="bash">
-btrfs property set -ts /mnt/@nixos_snapshot_202302 ro false
+btrfs property set -ts /snapshots/home_snapshot_202302 ro false
+</syntaxhighlight>
+However, changing read-only property of a snapshot in-place may [//lore.kernel.org/linux-btrfs/06e92a0b-e71b-eb21-edb5-9d2a5513b718@gmail.com/ causes issues] with any future incremental send/receive.
+Instead, a read-only snapshot itself (being a simple subvolume) can be snapshoted again as a read-write snapshot like this:
+<syntaxhighlight lang="bash">
+btrfs subvolume snapshot /snapshots/home_snapshot_202302 /snapshots/home_snapshot_202302_rw
 </syntaxhighlight>
-List snapshots for <code>/</code>
+Or it can be restored directly to <code>/home</code> straight away like this:
+{{warning|1=this will delete current <code>/home</code> and restore the snapshot! <code>/home</code> must be unmounted for this operation}}
 <syntaxhighlight lang="bash">
-sudo btrfs subvolume list /
+btrfs subvolume delete /home
+btrfs subvolume snapshot /snapshots/home_snapshot_202302 /home
 </syntaxhighlight>
+After this you can mount <code>/home</code> again.
 === Transfer snapshot ===
-Sending the snapshot <code>/mnt/@nixos_snapshot_202302</code> compressed to a remote host via ssh at <code>root@192.168.178.110</code> and saving it to a subvolume mounted or directory at <code>/mnt/nixos</code>
+Sending the snapshot <code>/snapshots/nixos_snapshot_202302</code> compressed to a remote host via ssh at <code>root@192.168.178.110</code> and saving it to a subvolume mounted or directory at <code>/mnt/nixos</code>
 <syntaxhighlight lang="bash">
-sudo btrfs send /mnt/@nixos_snapshot_202302 | zstd | ssh root@192.168.178.110 'zstd -d | btrfs receive /mnt/nixos'
+sudo btrfs send /snapshots/nixos_snapshot_202302 | zstd | ssh root@192.168.178.110 'zstd -d | btrfs receive /mnt/nixos'
 </syntaxhighlight>
 [[Category: Configuration]]
 [[Category:Filesystem]]