During a host failure, ESXi must be able to save diagnostic information to a preconfigured location for diagnostic and technical support purposes.
Typically, a partition to collect diagnostic information, also called VMkernel core dump, is created on a local storage device during ESXi installation. You can override this default behavior if, for example, you use shared storage devices instead of local storage. To prevent automatic formatting of local devices, detach the devices from the host before you install ESXi and power on the host for the first time. You can later set up a location for collecting diagnostic information on a local or remote storage device.
When you use storage devices, you can select between two options of setting up core dump collection. You can use a preconfigured diagnostic partition on a storage device or use a file on a VMFS datastore.