Technical information

VMware, Inc. 11
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This chapter provides guidance on selecting and configuring hardware for use with VMware vSphere.
Validate Your Hardware
 Test system memory for 72 hours, checking for hardware errors.
 Verify that all hardware in the system is on the hardware compatibility list for the VMware ESX version
you will be running.
 Make sure that your hardware meets the minimum configuration supported by the VMware ESX version
you will be running.
Hardware CPU Considerations
 When purchasing hardware, it is a good idea to consider CPU compatibility for VMware VMotion and
VMware Fault Tolerance. See “VMware vCenter Best Practices” on page 36.
Hardware-Assisted Virtualization
Many recent processors from both Intel and AMD include hardware features to assist virtualization. These
features were released in two generations: the first generation introduced CPU virtualization; the second
generation included CPU virtualization and added memory management unit (MMU) virtualization. For the
best performance, make sure your system uses processors with second-generation hardware-assist features.
Hardware-Assisted CPU Virtualization (Intel VT-x and AMD AMD-V)
The first generation of hardware virtualization assistance, VT-x from Intel and AMD-V from AMD, became
available in 2006. These technologies automatically trap sensitive calls, eliminating the overhead required to
do so in software. This allows the use of a hardware virtualization (HV) virtual machine monitor (VMM) as
opposed to a binary translation (BT) VMM.
Hardware-Assisted MMU Virtualization (Intel EPT and AMD RVI)
Some recent processors also include a new feature that addresses the overheads due to memory management
unit (MMU) virtualization by providing hardware support to virtualize the MMU. ESX 4.0 supports this
feature in both AMD processors, where it is called rapid virtualization indexing (RVI) or nested page tables
(NPT), and in Intel processors, where it is called extended page tables (EPT).
Without hardware-assisted MMU virtualization, the guest operating system maintains guest virtual memory
to guest physical memory address mappings in guest page tables, while ESX maintains “shadow page tables”
that directly map guest virtual memory to host physical memory addresses. These shadow page tables are
maintained for use by the processor and are kept consistent with the guest page tables. This allows ordinary
memory references to execute without additional overhead, since the hardware translation lookaside buffer
(TLB) will cache direct guest virtual memory to host physical memory address translations read from the
shadow page tables. However, extra work is required to maintain the shadow page tables.
Hardware for Use with VMware
vSphere
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