Unlike esxtop, which collects real-time data, the vscsiStats tool is used to gather the I/O statistics of a VM at a per-virtual-disk (VMDK) level. It can collect statistics such as the number of outstanding I/Os, size of the I/Os, and seek distance and latency. These statistics can be used in workload characterization. Understanding the characteristics of a workload will aid you in assigning the correct storage resources for virtual machines. For instance, if you have different datastores categorized into different storage tiers, then having a clear understanding of the I/O characteristics will facilitate the efficient placement of VMs.
The whitepaper, Storage Workload Characterization and Consolidation in Virtualized Environments, is a very interesting read on the study that was conducted. You can find it at https://communities.vmware...
