fix(system-backup): skip backup if it is a DR volume (#3487)

ref: longhorn/longhorn 6027, 9330, 10239

Signed-off-by: James Lu <james.lu@suse.com>

controller/system_backup_controller.go

@@ -799,6 +799,13 @@ func (c *SystemBackupController) backupVolumesIfNotPresent(systemBackup *longhor
 
 	volumeBackups := make(map[string]*longhorn.Backup, len(volumes))
 	for _, volume := range volumes {
+		// Don't need to create volume data backup for DR volumes since it will
+		// be restored from the source volume's backup.
+		if volume.Status.IsStandby {
+			c.logger.Infof("Skip backup for standby volume %v", volume.Name)
+			continue
+		}
+
 		volumeBackupName := bsutil.GenerateName("system-backup")
 
 		snapshot, err := c.createVolumeSnapshot(ctx, volume, volumeBackupName)