How to measure IO bottleneck when tuning Oracle

HI,
I have a high performance computer with large RAM and high speed CPU running OLTP.
But it only has a nomal speed hard disk.
I try to measure Oracle performance on my computer with TPCC.
The computer have large RAM, so at first, the average of transaction per minute could be a high value, like 40000 tpmC.
After a while, when the checkpoint comes , Oracle has to write the dirty data to the disk. then Oracle holds on and has no response till the data is writed to the disk.
So I think it is too many requirements from the client, and the oracle processes too many requirements, but the IO limits the performance.
So I want to reduce the requirements from the client to avoid no response from Oracle.
But I have try many ways,I still could not find the balance between requirements nmber and IO speed.
Could you give some suggestions about how to match the requirements nmber to IO speed ? Thanks~
By the way, I was using Oracle Enterprise Manager, but I could't understand the pictures on the Performance Page of OEM.
Is There any material about the meaning of the pictures on the Performance Page of OEM ? Thanks~
Oracle Version : 11g
Edited by: obsidianhom on 2011-1-14 上午9:05

You, won't tell us the OS flavor you are using.
And how did you measure IO also counts. If you generate awr report when system was too busy then what are the major waits do you see. May be it's not related to IO.

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