Technical information

Performance Best Practices for VMware vSphere 4.0
32 VMware, Inc.
Guest Operating System Storage Considerations
 The default storage adapter in ESX 4.0 is either BusLogic or LSILogic, depending on the guest operating
system. However, ESX 4.0 also includes a new virtual storage adapter, paravirtualized SCSI (PVSCSI, also
called VMware Paravirtual). PVSCSI adapters offer a significant reduction in CPU utilization as well as
potentially increased throughput compared to the BusLogic or LSILogic virtual storage adapters, and are
thus the best choice for environments with very I/O-intensive guest applications.
 If you choose to use the BusLogic virtual SCSI adapter, and are using a Windows guest operating system,
you should use the custom BusLogic driver included in the VMware Tools package.
 The depth of the queue of outstanding commands in the guest operating system SCSI driver can
significantly impact disk performance. A queue depth that is too small, for example, limits the disk
bandwidth that can be pushed through the virtual machine. See the driver-specific documentation for
more information on how to adjust these settings.
 Large I/O requests issued by applications in the guest can be split by the guest storage driver. Changing
the guest registry settings to issue larger block sizes can eliminate this splitting, thus enhancing
performance. For additional information see KB article 9645697, listed in “Related Publications” on
page 8.
 Make sure the system partitions within the guest are aligned. For further information you might want to
refer to the literature from the operating system vendor regarding appropriate tools to use as well as
recommendations from the array vendor.
N
OTE In order to use PVSCSI, your virtual machine must be using virtual hardware version 7, as
described in “ESX General Considerations” on page 17.