When you power on 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 defaults. By default, all visible blank internal disks are formatted with VMFS, so you can store virtual machines on the disks.

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 makes use of such disks, in particular if you are using logical volume manager (LVM) instead of (or in addition to) conventional partitioning schemes, ESXi could cause local LVM to be reformatted. Be sure to back up your system data before you power on ESXi for the first time.

On the hard drive or USB device from which the ESXi host is booting, the disk-formatting software retains existing diagnostic partitions that are created by the hardware vendor. In the remaining space, the software creates these partitions:

One 4GB VFAT scratch partition for system swap, if this partition is not present on another disk. See About the Scratch Partition.

One VMFS3 partition on the remaining free space.

The VFAT scratch partition is created only on the disk from which the ESXi host is booting. On the other disks, the software creates a VMFS3 partition on each disk spanning the whole disk.

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.

During ESXi installation, the installer creates a 110MB diagnostic partition for core dumps.

You might want to override this default behavior if, for example, your policy is to use shared storage devices instead of local storage. To prevent automatic disk formatting, detach the local storage devices from the host before you install ESXi and power on the host for the first time (or before you power on the host after you reset the host to the configuration defaults).

Automatic disk formatting occurs the first time you power on the host and when you power on the host after you reset the host to the configuration defaults. For subsequent reboots, you do not need to detach the local storage devices. If automatic disk formatting already occurred and you want to override the VMFS formatting, you can remove the datastore. See the Server Configuration Guide.