restic/system: Enable compression

Fixes #66.

machines/renge/configuration.nix

@@ -62,6 +62,7 @@
     enable = true;
     startAt = [ ]; # triggered by restic system backup
     location = "/var/lib/postgresql-backup";
+    compression = "none";
   };
   systemd.services.restic-backups-system = {
     after = [ "postgresqlBackup.service" ];

modules/restic/system.nix

@@ -87,6 +87,7 @@ in
         "/var"
       ] ++ cfg.extraPaths;
       extraBackupArgs = [
+        "--compression auto"
         "--exclude-caches"
         "--exclude-file=${excludesFile}"
         "--tag system"
@@ -113,6 +114,7 @@ in
         "sftp.command='ssh -i ${config.sops.secrets.restic-ssh-key.path} -p ${toString sftpPort} ${sftpTarget} -s sftp'"
       ];
       pruneOpts = [
+        "--compression auto"
         "--keep-daily 7"
         "--keep-monthly 12"
         "--keep-weekly 5"