There are many options related to monitoring your vSphere environment, but most commonly you will use the performance monitoring capabilities of vCenter Server. There is an option to monitor your VMs directly from the ESXi web client, but as you have already learned, ESXi hypervisor does not contain a database, thus performance data is only available for the past 60 minutes. Anything older is automatically discarded. On the other hand, with vCenter Server, you can store performance data for years.