Btrfs: Difference between revisions

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=== Scrubbing ===

Btrfs ~~filesystem~~ by default ~~keeps~~ checksums for all files, ~~and this allows~~ to ~~check~~ if ~~contents of~~ the file has ~~not~~ changed due to hardware malfunctions ~~and~~ other external effects.

Btrfs filesystems by default keep checksums for all files, to monitor if the file has changed due to hardware malfunctions or other external effects.

Scrubbing - is the process of checking file consistency ~~(for this it~~ may use checksums and/or duplicated copies of data, from raid for example). Scrubbing may be done "online", meaning you don't need to unmount a subvolume to scrub it.

Scrubbing is the process of checking file consistency, which may use checksums and/or duplicated copies of data, from raid for example. Scrubbing may be done "online", meaning you don't need to unmount a subvolume to scrub it.

You can enable automatic scrubbing ~~with~~

You can enable automatic scrubbing withː

services.btrfs.autoScrub.enable = true;

</syntaxhighlight>

Automatic scrubbing by default is performed once a month, but you can change that ~~with~~

Automatic scrubbing by default is performed once a month, but you can change that withː

services.btrfs.autoScrub.interval = "weekly";

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<code>interval</code> syntax is defined by [https://www.freedesktop.org/software/systemd/man/systemd.time.html#Calendar%20Events systemd.timer's Calendar Events]

By default, autoscrub will scrub all detected btrfs mount points. However, in case of mounted nested subvolumes (~~like in~~ example above <code>/nix</code> and <code>/home</code> are nested subvolumes under <code>/</code>), you only need to scrub the ~~top-most~~ one. So an example configuration may look like this:

By default, autoscrub will scrub all detected btrfs mount points. However, in case of mounted nested subvolumes (e.g. the example above where <code>/nix</code> and <code>/home</code> are nested subvolumes under <code>/</code>), you only need to scrub the topmost one. So an example configuration may look like this:

services.btrfs.autoScrub = {

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</syntaxhighlight>

The result of periodic auto scrub will be ~~save~~ to system journal, ~~however~~ you can ~~also always~~ check the status of the last ~~scrub with~~

The result of the periodic auto scrub will be saved to the system journal, and you can check the status of the last scrubː

btrfs scrub status /

</syntaxhighlight>

You can also start a ~~scrubbing~~ in background ~~manually~~

You can also start a scrub in the background manuallyː

btrfs scrub start /

</syntaxhighlight>

You can check the status of the ongoing scrubbing process with the same <code>status</code> command ~~from~~ above

You can check the status of the ongoing scrubbing process with the same <code>status</code> command as above.

=== Deduplication ===

Files with (partially) equal contents can be deduplicated using [https://github.com/Zygo/bees bees] or [https://github.com/markfasheh/duperemove duperemove].

bees can be configured in <code>configuration.nix</code>:

@@ Line 84: / Line 84: @@
 === Scrubbing ===
-Btrfs filesystem by default keeps checksums for all files, and this allows to check if contents of the file has not changed due to hardware malfunctions and other external effects.
+Btrfs filesystems by default keep checksums for all files, to monitor if the file has changed due to hardware malfunctions or other external effects.
-Scrubbing - is the process of checking file consistency (for this it may use checksums and/or duplicated copies of data, from raid for example). Scrubbing may be done "online", meaning you don't need to unmount a subvolume to scrub it.
+Scrubbing is the process of checking file consistency, which may use checksums and/or duplicated copies of data, from raid for example. Scrubbing may be done "online", meaning you don't need to unmount a subvolume to scrub it.
-You can enable automatic scrubbing with
+You can enable automatic scrubbing withː
 <syntaxhighlight lang="nix">
 services.btrfs.autoScrub.enable = true;
 </syntaxhighlight>
-Automatic scrubbing by default is performed once a month, but you can change that with
+Automatic scrubbing by default is performed once a month, but you can change that withː
 <syntaxhighlight lang="nix">
 services.btrfs.autoScrub.interval = "weekly";
@@ Line 99: / Line 99: @@
 <code>interval</code> syntax is defined by [https://www.freedesktop.org/software/systemd/man/systemd.time.html#Calendar%20Events systemd.timer's Calendar Events]
-By default, autoscrub will scrub all detected btrfs mount points. However, in case of mounted nested subvolumes (like in example above <code>/nix</code> and <code>/home</code> are nested subvolumes under <code>/</code>), you only need to scrub the top-most one. So an example configuration may look like this:
+By default, autoscrub will scrub all detected btrfs mount points. However, in case of mounted nested subvolumes (e.g. the example above where <code>/nix</code> and <code>/home</code> are nested subvolumes under <code>/</code>), you only need to scrub the topmost one. So an example configuration may look like this:
 <syntaxhighlight lang="nix">
 services.btrfs.autoScrub = {
@@ Line 108: / Line 108: @@
 </syntaxhighlight>
-The result of periodic auto scrub will be save to system journal, however you can also always check the status of the last scrub with
+The result of the periodic auto scrub will be saved to the system journal, and you can check the status of the last scrubː
 <syntaxhighlight lang="bash">
 btrfs scrub status /
 </syntaxhighlight>
-You can also start a scrubbing in background manually
+You can also start a scrub in the background manuallyː
 <syntaxhighlight lang="bash">
 btrfs scrub start /
 </syntaxhighlight>
-You can check the status of the ongoing scrubbing process with the same <code>status</code> command from above
+You can check the status of the ongoing scrubbing process with the same <code>status</code> command as above.
 === Deduplication ===
 Files with (partially) equal contents can be deduplicated using [https://github.com/Zygo/bees bees] or [https://github.com/markfasheh/duperemove duperemove].
 bees can be configured in <code>configuration.nix</code>: