DB2 - How to estimate proper BUFFERPOOL size? DB2 9.7.
8GB RAM on server.
Currently BP  has 500 MB (number of pages*pagesize)
Database has issue with increased IOPS.
So we think maybe BP should be increased.
How to estimate needed size for BP? Is there some recommendation? Maybe I would like to  put it on 1GB. What can be negative effect? Is it always greater better for BP?
You can't "estimate" the size of a buffer pool, because the answer is, "it depends".

Try using the AUTOCONFIGURE command to get started, and enable STMM.  Together these will go a long way towards getting your database running more efficiently.

I would also recommend you spend some time reading about DB2 Performance Tuning.  There is a ton of information available on the web, starting from the entire Performance Tuning section of the manual.