We have a vSphere 4.0 environment. We are having some disk I/O issues with a couple of VMs on an iSCSI array. We believe that we know what the issue is and how to fix it. But before we implement the fix, we'd like to get a baseline of what the disk I/O is now and then what it is after the change. We originally determined the issue by running perfmon's on the VM, but would like some other utility that we could run that might be "better". And we'd like this to be one that would monitor other aspects of the virtual environment.
Free would be good, but I'm not opposed to paying for something either.