Hi Narasimhan,
Besides Juergen suggestion you may refer to SAP Note 1887068 - SYB: Using external backup and restore with SAP Sybase ASE for more details about the "quiesce database".
Please ensure that the directories mentioned on that note are backuped up ("item Copy all device files of all the databases you quiesced."). Additionally please refer to SAP Note 1585981 - SYB: Ensuring Recoverability for SAP ASE .
Best regards,
Victoria.