Make sure the host meets the minimum hardware configurations supported by ESXi 5.5.

Hardware and System Resources

To install and use ESXi 5.5, your hardware and system resources must meet the following requirements:

  • Supported server platform. For a list of supported platforms, see the VMware Compatibility Guide at
  • ESXi 5.5 will install and run only on servers with 64-bit x86 CPUs.
  • ESXi 5.5 requires a host machine with at least two cores.
  • ESXi 5.5 supports only LAHF and SAHF CPU instructions.
  • ESXi 5.5 requires the NX/XD bit to be enabled for the CPU in the BIOS.
  • ESXi supports a broad range of x64 multicore processors. For a complete list of supported processors, see the VMware compatibility guide at
  • ESXi requires a minimum of 4GB of physical RAM. Provide at least 8GB of RAM to take full advantage of ESXi features and run virtual machines in typical production environments.
  • To support 64-bit virtual machines, support for hardware virtualization (Intel VT-x or AMD RVI) must be enabled on x64 CPUs.
  • One or more Gigabit or 10Gb Ethernet controllers. For a list of supported network adapter models, see the VMware Compatibility Guide at
  • Any combination of one or more of the following controllers:
    • Basic SCSI controllers. Adaptec Ultra-160 or Ultra-320, LSI Logic Fusion-MPT, or most NCR/Symbios SCSI.
    • RAID controllers. Dell PERC (Adaptec RAID or LSI MegaRAID), HP Smart Array RAID, or IBM (Adaptec) ServeRAID controllers.
  • SCSI disk or a local, non-network, RAID LUN with unpartitioned space for the virtual machines.
  • For Serial ATA (SATA), a disk connected through supported SAS controllers or supported on-board SATA controllers. SATA disks will be considered remote, not local. These disks will not be used as a scratch partition by default because they are seen as remote.
    Note: You cannot connect a SATA CD-ROM device to a virtual machine on an ESXi 5.5 host. To use the SATA CD-ROM device, you must use IDE emulation mode.

Storage Systems

For a list of supported storage systems, see the VMware Compatibility Guide at ESXi 5.5 supports installing on and booting from the following storage systems:

  • SATA disk drives. SATA disk drives connected behind supported SAS controllers or supported on-board SATA controllers.

    Supported SAS controllers include:

    • LSI1068E (LSISAS3442E)
    • LSI1068 (SAS 5)
    • IBM ServeRAID 8K SAS controller
    • Smart Array P400/256 controller
    • Dell PERC 5.0.1 controller

    Supported on-board SATA include:

    • Intel ICH9
    • NVIDIA MCP55
    • ServerWorks HT1000
    Note: ESXi does not support using local, internal SATA drives on the host server to create VMFS datastores that are shared across multiple ESXi hosts.
  • Serial Attached SCSI (SAS) disk drives. Supported for installing ESXi and for storing virtual machines on VMFS partitions.
  • Dedicated SAN disk on Fibre Channel or iSCSI
  • USB devices. Supported for installing ESXi.
  • Software Fibre Channel over Ethernet (FCoE). See Installing and Booting ESXi with Software FCoE.

ESXi Booting Requirements

vSphere 5.5 supports booting ESXi hosts from the Unified Extensible Firmware Interface (UEFI). With UEFI you can boot systems from hard drives, CD-ROM drives, or USB media. Network booting or provisioning with VMware Auto Deploy requires the legacy BIOS firmware and is not available with UEFI.

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

Note: Changing the boot type from legacy BIOS to UEFI after you install ESXi 5.5 might cause the host to fail to boot. In this case, the host displays an error message similar to: Not a VMware boot bank. Changing the host boot type between legacy BIOS and UEFI is not supported after you install ESXi 5.5.

Storage Requirements for ESXi 5.5 Installation

Installing ESXi 5.5 requires a boot device that is a minimum of 1GB in size. When booting from a local disk or SAN/iSCSI LUN, a 5.2GB disk is required to allow for the creation of the VMFS volume and a 4GB scratch partition on the boot device. If a smaller disk or LUN is used, the installer will attempt to allocate a scratch region on a separate local disk. If a local disk cannot be found the scratch partition, /scratch, will be located on the ESXi host ramdisk, linked to /tmp/scratch. You can reconfigure /scratch to use a separate disk or LUN. For best performance and memory optimization, VMware recommends that you do not leave /scratch on the ESXi host ramdisk.

To reconfigure /scratch, see Set the Scratch Partition from the vSphere Web Client.

Due to the I/O sensitivity of USB and SD devices the installer does not create a scratch partition on these devices. When installing on USB or SD devices, the installer attempts to allocate a scratch region on an available local disk or datastore. If no local disk or datastore is found, /scratch is placed on the ramdisk. After the installation, you should reconfigure /scratch to use a persistent datastore. Although a 1GB USB/SD device will suffice for a minimal installation, VMware strongly recommends using a 4GB or larger USB/SD device. The extra space will be used for an expanded coredump partition on the USB/SD device. VMware recommends using a high quality USB flash drive of 16GB or larger so that the extra flash cells can prolong the life of the boot media, but high quality drives of 4GB or larger are sufficient to hold the extended coredump partition. See Knowledge Base article 2004784.

In Auto Deploy installations, the installer attempts to allocate a scratch region on an available local disk or datastore. If no local disk or datastore is found /scratch is placed on ramdisk. You should reconfigure /scratch to use a persistent datastore following the installation.

For environments that boot from a SAN or use Auto Deploy, it is not necessary to allocate a separate LUN for each ESXi host. You can co-locate the scratch regions for many ESXi hosts onto a single LUN. The number of hosts assigned to any single LUN should be weighed against the LUN size and the I/O behavior of the virtual machines.