Update modules/ROOT/pages/backup-restore/online-backup.adoc

Author: NataliaIvakina

modules/ROOT/pages/backup-restore/online-backup.adoc

@@ -377,6 +377,10 @@ When enabled, the DBMS automatically selects the most appropriate servers to act
 By default, the online backup command requires the user to determine which servers host the target database and direct the command to one of them.
 With remote address resolution enabled, the DBMS performs this mapping automatically, removing the need for manual server selection.
 
+The server selection occurs in the following order:
+* The DBMS first selects all servers hosting the database in secondary mode.
+* If it is not possible to back up from one of the secondaries, the DBMS attempts to take a backup from the primary followers before finally trying the database primary writer.
+
 
 [[online-backup-example]]
 == Examples