Storage optimization: Difference between revisions

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== Moving the store ==

{{ic|/nix}} can reside on another device. This is useful if your root device is very small, and that you have another, larger drive at hand. ~~It is easiest to set up when installing NixOS. To move <code>/nix</code> to another device on an existing NixOS installation:~~

{{ic|/nix}} can reside on another device. This is useful if your root device is very small, and that you have another, larger drive at hand.

# Create a new ~~ext4~~ partition and mount it over <code>/mnt</code>

If the second mountpoint is on the same device, some benefit can still be gained by formatting the partition it points to with a different file system. For example: on a Raspberry Pi, f2fs could possibly be used for a gain in I/O throughput.

Regardless of <code>/nix</code>'s filesystem, it can also be mounted with <code>noatime</code> (as seen in the example below). This will reduce metadata writes, improving I/O and the device's lifespan.

This is easiest to set up while installing NixOS, but <code>/nix</code> can be moved on a live system:

# Create a new partition and mount it over <code>/mnt</code>

# <code>rsync -aAxv</code> everything from <code>/nix</code> to <code>/mnt</code>

# bind <code>/mnt</code> to <code>/nix</code> (e.g. using <code>mount</code>).

# Restart nix daemon with <code>systemctl restart nix-daemon.service </code> <code>systemctl restart nix-daemon.socket </code>.

# Rerun <code>nixos-rebuild switch</code> with something like <syntaxhighlight lang="bash">fileSystems."/nix" = { device = "/dev/disk/by-label/nix"; neededForBoot = true; options = [ "noatime" ]; };</syntaxhighlight>

# reboot to be sure <code>/nix/store</code> is properly mounted.

# Once you are sure everything works, you can delete the old store doing a bind mount <code>/</code> to <code>/old_root</code>, and remove <code>/old_root/nix</code>.

Keep in mind that all commands like <code>mount</code> and <code>bash</code> point to some executable in <code>/nix/store</code>, so never mount an empty disk over <code>/nix</code> or <code>/nix/store</code>, otherwise you will be locked out until reboot!

@@ Line 118: / Line 118: @@
 == Moving the store ==
-{{ic|/nix}} can reside on another device. This is useful if your root device is very small, and that you have another, larger drive at hand. It is easiest to set up when installing NixOS. To move <code>/nix</code> to another device on an existing NixOS installation:
+{{ic|/nix}} can reside on another device. This is useful if your root device is very small, and that you have another, larger drive at hand.
-# Create a new ext4 partition and mount it over <code>/mnt</code>
+If the second mountpoint is on the same device, some benefit can still be gained by formatting the partition it points to with a different file system. For example: on a Raspberry Pi, f2fs could possibly be used for a gain in I/O throughput.
+Regardless of <code>/nix</code>'s filesystem, it can also be mounted with <code>noatime</code> (as seen in the example below). This will reduce metadata writes, improving I/O and the device's lifespan.
+This is easiest to set up while installing NixOS, but <code>/nix</code> can be moved on a live system:
+# Create a new partition and mount it over <code>/mnt</code>
 # <code>rsync -aAxv</code> everything from <code>/nix</code> to <code>/mnt</code>
 # bind <code>/mnt</code> to <code>/nix</code> (e.g. using <code>mount</code>).
 # Restart nix daemon with <code>systemctl restart nix-daemon.service </code> <code>systemctl restart nix-daemon.socket </code>.
 # Rerun <code>nixos-rebuild switch</code> with something like <syntaxhighlight lang="bash">fileSystems."/nix" = { device = "/dev/disk/by-label/nix";  neededForBoot = true; options = [ "noatime" ]; };</syntaxhighlight>
 # reboot to be sure <code>/nix/store</code> is properly mounted.
 # Once you are sure everything works, you can delete the old store doing a bind mount <code>/</code> to <code>/old_root</code>, and remove <code>/old_root/nix</code>.
 Keep in mind that all commands like <code>mount</code> and <code>bash</code> point to some executable in <code>/nix/store</code>, so never mount an empty disk over <code>/nix</code> or <code>/nix/store</code>, otherwise you will be locked out until reboot!