Sizing the Virtual Hard Disk

For I/O Analyzer worker VMs, it's recommended to create a larger second virtual hard disk which serves as the IOmeter target.

Is the size of the virtual Hard Disk exactly the same as the workload's working set size, that is, that all of the data in the virtual disk is read or written to storage during the run?

Do you have any other recommendations in deciding how large the second virtual hard disk should be for a worker VM?

Thank you,

Rebecca