During the autoconfiguration phase, a 4GB VFAT scratch partition is created if the partition is not present on another disk.

When ESXi boots, the system tries to find a suitable partition on a local disk to create a scratch partition.

The scratch partition is not required. It is used to store vm-support output, which you need when you create a support bundle. If the scratch partition is not present, vm-support output is stored in a ramdisk. This might be problematic in low-memory situations, but is not critical.

For ESXi Installable, the partition is created during installation and is thus selected. VMware recommends that you leave it unchanged.