One of the beauties of a thin hypervisor architecture like VMware ESXi is the fact that the entire state of the system can be described in a much more compact fashion than is possible with a general-purpose operating system.  This include areas such as: virtual networking configuration, storage settings, and host infrastructure services such as NTP and logging.  All changes to the system occur through well-defined APIs, so it's easy to know what can be modified.

This fact, among other things, makes it easy to back up the entire state of an ESXi host, in case you later need to restore the system to the same state.  The vCLI (vSphere Command Line Interface) has a command specially built for this purpose: vicfg-cfgbackup.  A recent blog posting on goes over a real-life situation where this command proved invaluable.:

A client had an ESXi host where the USB drive failed….. We needed to get this failed ESX host back online and quick!

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