It happened last night, probably after hotbackup. One of our system data file size increased from 1.9G to 2.8G on the o/s level. But dba_data_file still shows this file is 1.9G and has 50% space left.
There is no error in alert.log file or any dump file.
Right now the database is still running fine. Please advise whether this is an o/s issue or database issue.
We are using 8.1.7 on HP Unix 11i 9000.

I appreciate your help.