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VMware ACE Administrator’s Manual
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 a
virtual machine using IDE virtual disks on a multiprocessor host computer. 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.
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 6a. Download DMACHECK.EXE from the Microsoft Web site
(support.microsoft.com/support/kb/articles/Q191/7/74.ASP) and run it.
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.