nixbld: also store backups on zfs tank

nixbld-etc-nixos/backup-module.nix

@@ -7,6 +7,8 @@ let
     set -e
     umask 0077
 
+    FILENAME=backup-`date +%F`.tar.bz2.gpg
+
     DBDUMPDIR=`mktemp -d`
     pushd $DBDUMPDIR
 
@@ -16,7 +18,8 @@ let
     ${pkgs.gnutar}/bin/tar cf - --exclude "/var/lib/gitea/repositories/*/*.git/archives" /etc/nixos /var/lib/gitea flarum.sql mattermost.sql | \
         ${pkgs.bzip2}/bin/bzip2 | \
         ${pkgs.gnupg}/bin/gpg --symmetric --batch --passphrase-file /etc/nixos/secret/backup-passphrase | \
-        ${pkgs.rclone}/bin/rclone rcat --config /etc/nixos/secret/rclone.conf dropbox:backup-`date +%F`.tar.bz2.gpg
+        tee --output-error=warn /tank/backup/$FILENAME | \
+        ${pkgs.rclone}/bin/rclone rcat --config /etc/nixos/secret/rclone.conf dropbox:$FILENAME
 
     popd
     rm -rf $DBDUMPDIR