Hi Yeshwanth ,
Apologies .. not good at Linux commands
Can you try df -h
The core is if your filesystems ( /db2/PR3/sapdata[1-4] ) has enough space you dont need to worry [ believe you are not getting any errors in SM21 /db2diag ] , DB2 will automatically extend .
If all the File systems are getting filled up extend your FS ( this is the easiest option as far i know )
You may also extend as suggested by siddesh/Frank
Thanks ,
Manu