When you start ESXi, the host enters an autoconfiguration phase during which system storage devices are configured with defaults.

When you reboot the ESXi host after installing the ESXi image, the host configures the system storage devices with default settings. Starting with ESXi 7.0, you can activate the option autoPartition, which automatically formats all available empty devices with VMFS, except for legacy SD and USB devices. The default is autoPartition=FALSE, which formats with VMFS only boot devices with size larger than 128 GB. For more information, see VMware knowledge base article 77009.

Caution: ESXi overwrites any disks that appear to be blank. Disks are considered to be blank if they do not have a valid partition table or partitions. If you are using software that uses such disks, in particular if you are using logical volume manager (LVM) instead of, or in addition to, conventional partitioning schemes, ESXi might cause local LVM to be reformatted. Back up your system data before you power on ESXi for the first time.

On the hard drive or USB device that the ESXi host is booting from, the disk-formatting software retains existing diagnostic partitions that the hardware vendor creates. In the remaining space, the software creates the partitions described below.

Partitions Created by ESXi on the Host Drive

For fresh installations, several new partitions are created for the system boot, boot banks, and ESX-OSData. Fresh ESXi installations use GUID Partition Tables (GPT) instead of MSDOS-based partitioning. The installer creates boot banks of varying size depending on the size of the disk. For more information on the scratch partition see About the Scratch Partition.

The installer affects only the installation disk. The installer does not affect other disks of the server. When you install on a disk, the installer overwrites the entire disk. When the installer autoconfigures storage, the installer does not overwrite hardware vendor partitions.

To create the VMFS datastore, the ESXi installer requires a minimum of 128 GB of free space on the installation disk.

You might want to override this default behavior if, for example, you use shared storage devices instead of local storage. To prevent automatic disk formatting, detach the local storage devices from the host under the following circumstances:
  • Before you start the host for the first time.
  • Before you start the host after you reset the host to the configuration defaults.

To override the VMFS formatting if automatic disk formatting already occurred, you can remove the datastore. See the vCenter Server and Host Management documentation.