• Install snapbtr

There is a number of different helpers for the automatic snapshoting a btrfs volume. Assuming that we want to create a snapshot before offlineimap syncs it’s data, the best place to call such a tool is hook scripts.

But almost all these helpers require root permission, which is not acceptable for us (unless you are running offlineimap as root).

The snapbtr fits this requirement. It separates creating snapshots (no root needed) from cleaning-up (root required).

To install, follow the instructions on the project page

  • Create a workspace

This approach requires serveral components. Let’s keep them together in one folder

mkdir ~/email && cd ~/email
  • Prepare the storage
touch btrfs.vol
truncate -s 20G btrfs.vol
mkfs.btrfs btrfs.vol
mkdir store
mkdir btrfs-root
sudo mount btrfs.vol  btrfs-root/
sudo btrfs subvolume create btrfs-root/email
sudo mount btrfs.vol store/ -o subvol=email
# It is very important to change the owner! Otherwise snapbtr would not
# be able to create snapshots
sudo chown yuri:yuri btrfs-root/ -R
mkdir btrfs-root/snapshots

In this setup, the “store” folder is inteded to keep your Maildir(s). So you would need to provide the path to it in your ~/.offlineimaprc file. For example:

[Repository gmail_local]
type = GmailMaildir
localfolders = ~/email/store/your_account@gmail.com

IMPORTANT: if you already had offlineimap configured with this account, you need to check if your offlineimap version is newer then 7.0.0. Or there is a high risk of wiping your emails on the server. Check the FAQ for more details.

  • Setup the hook

Create a script

cat > make_snapshot.sh <<EOF
snapbtr -s $HOME/email/store $HOME/email/btrfs-root/snapshots

chmod +x make_snapshot.sh

And, finally add the path to the hook script into your ~/.offlineimaprc file into the Account section. For example:

[Account gmail]
localrepository = gmail_local
remoterepository = gmail_remote
status_backend = sqlite
presynchook = ~/email/make_snapshot.sh

In this example we used offlineimap’s hook. However there are other options, because offlineimap is just an email fetcher, and usually there are more applications in the final email stack. For example, if you are using notmuch, much better way to make your snapshots would be using its “pre-new” hook. This way you will be backuping not only offlineimap’s data, but notmuch’s database as well.