Technical information

VMware, Inc. 29

This chapter provides guidance regarding the guest operating systems running in virtual machines.

Guest Operating System General Considerations

 Use guest operating systems that are supported by ESX. See the Guest Operating System Installation Guide

for a list.

 Install the latest version of VMware Tools in the guest operating system. Make sure to update VMware

Tools after each ESX upgrade.

Installing VMware Tools in Windows guests updates the BusLogic SCSI driver included with the guest

operating system to the VMware-supplied driver. The VMware driver has optimizations that

guest-supplied Windows drivers do not.

VMware Tools also includes the balloon driver used for memory reclamation in ESX. Ballooning

(described in “Memory Overcommit Techniques” on page 23) will not work if VMware Tools is not

installed.

 Disable screen savers and Window animations in virtual machines. On Linux, if using an X server is not

required, disable it. Screen savers, animations, and X servers all consume extra physical CPU resources,

potentially affecting consolidation ratios and the performance of other virtual machines.

 Schedule backups and anti-virus programs in virtual machines to run at off-peak hours, and avoid

scheduling them to run simultaneously in multiple virtual machines on the same ESX host. In general, it

is a good idea to evenly distribute CPU usage, not just across CPUs but also across time. For workloads

such as backups and antivirus where the load is predictable, this is easily achieved by scheduling the jobs

appropriately.

 For the most accurate timekeeping, consider configuring your guest operating system to use NTP,

Windows Time Service, or another timekeeping utility suitable for your operating system. The

time-synchronization option in VMware Tools can be used instead, but it is not designed for the same

level of accuracy as these other tools and does not adjust the guest time when it is ahead of the host time.

We recommend, however, that within any particular virtual machine you use either the VMware Tools

time-synchronization option, or another timekeeping utility, but not both.

Running Paravirtualized Operating Systems

ESX includes support for virtual machine interface (VMI), used for communication between the guest

operating system and the hypervisor, thus improving performance and efficiency. Enabling this support will

improve the performance of virtual machines running operating systems with VMI by reducing their CPU

utilization and memory space overhead (the later being especially true for SMP virtual machines). Even when

only some of the virtual machines on an ESX system use VMI, the performance of all virtual machines on that

server might benefit due to the hardware resources freed up for ESX to allocate elsewhere.

Guest Operating Systems

NOTE VMware Tools might not be available for unsupported guest operating systems.