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".
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.