diff --git a/btrfs.org b/btrfs.org
index e3adbcf..3cc44ea 100644
--- a/btrfs.org
+++ b/btrfs.org
@@ -1,6 +1,50 @@
 #+title: Btrfs
 #+setupfile: ../org-templates/page.org
 
+** Create systemd.mount unit for Btrfs on external HDD
+#+BEGIN_QUOTE
+internet_archive is used here as an example.
+#+END_QUOTE
+
+Get the UUID of the Btrfs partition.
+
+#+BEGIN_SRC shell
+sudo blkid -s UUID -o value /dev/sda1
+
+d3b5b724-a57a-49a5-ad1d-13ccf3acc52f
+#+END_SRC
+
+Edit ~/etc/systemd/system/mnt-internet_archive.mount.
+
+#+BEGIN_SRC systemd
+[Unit]
+Description=internet_archive Btrfs subvolume
+DefaultDependencies=yes
+
+[Mount]
+What=/dev/disk/by-uuid/d3b5b724-a57a-49a5-ad1d-13ccf3acc52f
+Where=/mnt/internet_archive
+Type=btrfs
+Options=subvol=@internet_archive,compress=zstd:1
+
+[Install]
+WantedBy=multi-user.target
+#+END_SRC
+
+- ~DefaultDependencies=yes~ : The mount unit automatically acquires ~Before=umount.target~ and ~Conflicts=umount.target~. Local filesystems automatically gain ~After=local-fs-pre.target~ and ~Before=local-fs.target~. Network mounts, such as NFS, automatically acquire ~After=remote-fs-pre.target network.target network-online.target~ and ~Before=remote-fs.target~.
+- ~Options=subvol=@internet_archive,compress=zstd:1~ : Use the subvolume ~@internet_archive~ and use zstd compression level 1.
+
+#+BEGIN_QUOTE
+Note that the name of the unit file, e.g. ~mnt-internet_archive.mount~, must correspond to the ~Where=/mnt/internet_archive~ directive, such that the filesystem path separator / in the ~Where~ directive is replaced by an en dash in the unit file name.
+#+END_QUOTE
+
+Reload the daemons and enable the mount unit.
+
+#+BEGIN_SRC shell
+sudo systemctl daemon-reload
+sudo systemctl enable --now mnt-internet_archive.mount
+#+END_SRC
+
 ** Setup encrypted external drive for backups
 *** Prepare the external drive
 #+begin_src shell