sysadmin/cassandra-upgrade: Before upgrading

docs/sysadm/data-silos/cassandra/upgrade.rst

@@ -43,6 +43,14 @@ Commit and push the changes.
 
 Connect to pergamon and deploy those changes.
 
+.. admonition:: Stop all repair jobs before upgrading
+   :class: warning
+
+   | All scheduled jobs must be paused and all running jobs must be stopped and aborted.
+   | You can perform these actions from the web UI `reaper <https://cassandra-reaper.io/docs/>`_.
+   | - `Reaper production <https://reaper.internal.softwareheritage.org/webui/login.html>`_
+   | - `Reaper staging <https://reaper.internal.staging.swh.network/webui/login.html>`_
+
 .. _manual_cassandra_upgrade:
 
 Manual procedure