Determining the boot device type and size for each ESXi host in the management domain of VMware Cloud Foundation is important for the creation of system storage volumes. You also plan the location of the scratch partition according to the selected boot device type so that system log information is available even if a storage failure occurs.

ESXi requires a boot disk of at least 8 GB for USB or SD devices, and 32 GB for other device types such as HDD, SSD, or NVMe. A boot device must not be shared between ESXi hosts.

ESXi can boot from a disk larger than 2 TB if the system firmware and the firmware on any add-in card support it. See vendor documentation.

The ESXi system storage volumes occupy up to 128 GB of disk space. A local VMFS datastore is only created if the local disk device has at least 4 GB additional free space. To share a boot device with a local VMFS datastore, you must use a local disk with space larger than 120 GB. If a local disk cannot be found, ESXi operates in a mode with limitations, where certain functionality is deactivated, and the scratch partition is on the RAM disk of the ESXi host, linked to the /tmp folder. As a result, log information and stack traces are lost on host reboot. You can reconfigure the scratch partition to use a separate disk or LUN.

An ESXi installation process on a USB or SD device does not configure a default scratch partition on the local disk. Place the scratch partition on a shared non-vSAN datastore and configure remote syslog logging for the ESXi host.

Table 1. Design Decisions on the Boot Device and Scratch Partition of the ESXi Hosts

Decision ID

Design Decision

Design Justification

Design Implication

VCF-MGMT-ESX-CFG-008

Install and configure all ESXi hosts in the default management cluster to boot using a 32-GB device or greater.

Provides hosts that have large memory, that is, greater than 512 GB, with enough space for the scratch partition when using vSAN.

When you use SATA-DOM or SD devices, scratch partition and ESXi logs are not retained locally. Configure the scratch partition of each ESXi host on supplemental storage.

VCF-MGMT-ESX-CFG-009

Use the default configuration for the scratch partition on all ESXi hosts in the default management cluster.

  • If a failure in the vSAN cluster occurs, the ESXi hosts remain responsive and log information is still accessible.

  • It is not possible to use vSAN datastore for the scratch partition.

When you use SATA-DOM or SD devices, scratch partition and ESXi logs are not retained locally. Configure the scratch partition of each ESXi host on supplemental storage.