In my alert log I have encounter some new messages which actually solve the issues for now and alert log it says “active session history performed an emergency flush this may mean that that a ASH is undersized if emergency flashes are a recurring issue both ASH size and the total number of emergency flashes since instant start-up can be monitored by running the following
select total_size ,Flash_emergency_count from v$ASH_ info
Once that message got a appeared I have successfully mounted the instance and then open the database on second node I have also checked my ASM and now I am able to connect to ASM instance as well so maybe the whole story was this flushing of ASH repository to whom it was saying that’s that -/u01 file system is full so please offer your comments as I am not sure that issue is completely resolved