For new installations of ESXi, during the autoconfiguration phase, a scratch partition is created as part of the ESX-OSDATA partition.
The scratch partition serves to store system logs, which you need when you create a support bundle. If the scratch partition is not present, system logs are stored in a ramdisk. If no scratch partition is created, you can configure one. You can also override the default configuration.
You can create the scratch partition on a remote SAN or NFS-mounted directory.