Apply Alex suggestions

Author: sinclert-canonical

docs/how-to/back-up-and-restore/create-a-backup.md

@@ -15,9 +15,18 @@ Once `juju status` shows Charmed MySQL as `active` and `idle`, you can create yo
 juju run mysql/leader create-backup
 ```
 
-If you have a cluster of one unit, you can run the `create-backup` action on `mysql-k8s/leader` (which will also be the primary unit). 
+If you have a cluster of one unit, you can run the `create-backup` action on the leader (which will also be the primary unit).
+Otherwise, you must run the `create-backup` action on a non-primary unit. To find the primary, see `juju status` or
+run `juju run mysql/leader get-cluster-status` to find the primary unit.
 
-Otherwise, you must run the `create-backup` action on a non-primary unit. To find the primary, see `juju status` or run `juju run mysql-k8s/leader get-cluster-status` to find the primary unit).
+The `create-backup` action validates that the unit in charge of the backup is healthy, by:
+- Checking that the MySQL cluster is in a valid state (`OK` or `OK_PARTIAL` from the InnoDB [cluster status](https://dev.mysql.com/doc/mysql-shell/8.0/en/monitoring-innodb-cluster.html))
+- Checking that the MySQL instance is in a valid state (`ONLINE` from Replication [member states](https://dev.mysql.com/doc/refman/8.0/en/group-replication-server-states.html).
+
+In order to override these precautions, use the `force` flag:
+```shell
+juju run mysql/leader create-backup force=True
+```
 
 ## List backups
 You can list your available, failed, and in progress backups by running the `list-backups` command: