How do I tell the actual IOPS used by Oracle? This is hopefully a simple question. We have a large DB deployment that we need to scale up over the next year. For scaling we have been relying on our vendor, but recent developments have caused us to doubt their ability to provide good information about the DB. So, what I'd like to do is go into oracle and see what actual IO numbers look like. Is there any easy way to do this?
There is no short answer to this question, the ways to monitor the behavior of an Oracle database depend on the tools available, your database edition, your database version, do you use ASM or a filesytem, etc.

A general approach that works for any database edition and version (that is from Oracle 8 on) is to install statspack (see http://www.orafaq.com/wiki/Statspack or the documentation in $ORACLE_HOME/rdbms/admin) and take snapshots.
The snapshots will be taken every hour by default so the data is aggregated over this period of time.  

This will give you an overview of the behavior of the database (e.g. amount of physical reads).

This is just a starting point as you may want to check, if your SAN partitions are correctly aligned, do your FS block size match the DB block size (8k by default) and so on.