Specifications

CHAPTER 6 Using Disks in a Virtual Machine
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Disk Performance in Windows NT
Guests on Multiprocessor Hosts
Some users have seen slower than expected disk input and output performance
when running Windows NT guest operating systems. They see the problem in GSX
Server virtual machines using IDE virtual disks on multiprocessor host computers. The
I/O issue is especially noticeable when the virtual machine is booting.
Note: Performance in Windows NT guest operating systems may also be affected by
disk fragmentation on the host computer. For details, see Configuring and
Maintaining the Host Computer in the VMware GSX Server Administration Guide.
Improving Performance
You may increase performance by enabling DMA (direct memory access) on the
virtual hard disk’s IDE channel in the virtual machine.
If you have a virtual disk and a DVD/CD-ROM attached as master and slave to the
primary IDE controller (channel 0) and you want to enable DMA, power off the virtual
machine and use the virtual machine settings editor (VM > Settings) to move the
DVD/CD-ROM drive to the secondary IDE controller (channel 1) at IDE 1:0.
You can enable the DMA feature after you finish installing Windows NT. You must
install Service Pack 3 or higher in the virtual machine to enable this option.
Once the virtual machine is running Windows NT, insert an SP3 or SP4 CD in the drive
and run DMACHECK.EXE from the \SUPPORT\UTILS\I386 folder on the CD. Or
download DMACHECK.EXE from the Microsoft Web site
(support.microsoft.com/support/kb/articles/Q191/7/74.ASP).
Click the Enabled option for the IDE controller and channel configured for the virtual
disk. Typically, this is channel 0 only, unless you have the virtual machine configured
with multiple virtual disks and no virtual DVD/CD-ROM drive.
As noted above, you should not enable DMA on an IDE channel with a virtual DVD/
CD-ROM drive attached.