Real-time and historical statistics

You can use vSphere Web Client to display two kinds of statistics:

• real-time statistics – information generated for the past hour at the 20-second specificity.
• historical statistics – information generated for the past day, week, month, or year, at varying specificities.

The real-time statistics are stored in a flat file on the ESXi host and in memory on the vCenter Server system. ESXi hosts collect the real-time statistics for the host and its virtual machines every 20 seconds.

The historical statistics are stored in the vCenter Server database. It is possible to configure how much statistical data is collected and stored.

The following table shows how much statistics are stored at different specificities (image source: VMware):

In the picture above you can see that past-day statistics show one data point every five minutes (288 samples), while past-year statistics show one data point per day (365 samples).