Debunking Microsoft Virtual Server myths

Myth #1: Disable hyperthreading.

According to Microsoft, it "was" recommended that you disable hyperthreading on your system because guest OSes can only utilize a single "logical" processor. If the host is set up to use hyperthreading, it presents two logical CPUs for every physical CPU installed because that CPU's total processing power is actually being split by hyperthreading (the process of handling two threads at one time via one CPU). As such, the guest OS will use only one of the "logical" CPUs and will only get half of the CPU when it is under load.

However, with the release of Virtual Server 2005 RC2, Microsoft apparently believes it has worked around this issue. To be honest, I am not quite sure how, since the article that Microsoft posted describing this issue did not go into specifics. But you can try turning on your hyperthreading and see if you get a performance boost while running multiple guest OSes.

Myth #2. Don't use the /3GB switch.

Regardless of the amount of physical memory in your system, Windows server (32-bit versions only and not applicable to Windows Standard Server) uses a virtual address space of 4 GB, with 2 GB allocated to user-mode processes (for example, applications) and 2 GB allocated to kernel-mode processes (for example, the operating system and kernel-mode drivers). On systems that have 1 GB or more of physical memory, a special startup switch /3GB can be used to allocate more memory to applications (3 GB) and less memory to the operating system (1 GB).

However, using the common /3GB switch may ca

Digg This!     StumbleUpon     Del.icio.us

RELATED CONTENT Windows Server Virtualization and Microsoft Hyper-V Hyper-V gains new resiliency features with Windows Server 2008 R2 Getting started with Windows PowerShell and Microsoft Hyper-V Hyper-V workarounds: How to ensure high availability Microsoft Hyper-V: Best practices for performance, backups and management Microsoft Hyper-V Management Tutorial Working with snapshots in Microsoft Hyper-V Running Hyper-V on Server Core Configuring virtual machines with Hyper-V Using the Microsoft Assessment and Planning Toolkit with Hyper-V Working with VHDs in Hyper-V Windows Server Monitoring and Management Simple tools and techniques for finding Windows memory leaks Top Windows server hardening standards and guidelines Hyper-V gains new resiliency features with Windows Server 2008 R2 Troubleshooting Windows print spooler crashes Windows server hardening: How much is enough? Terminal Services grows up with Windows Server 2008 R2 Top five Server Core management tips for Windows 2008 Windows Server 2008 R2: Not your father's R2 upgrade The bottom line on Microsoft Hyper-V Does Microsoft Hyper-V fit in the dynamic data center?

RELATED GLOSSARY TERMS Terms from Whatis.com − the technology online dictionary Microsoft Hyper-V version 1.0  (SearchWindowsServer.com)

RELATED RESOURCES 2020software.com, trial software downloads for accounting software, ERP software, CRM software and business software systems Search Bitpipe.com for the latest white papers and business webcasts Whatis.com, the online computer dictionary

use your system to have problems launching multiple virtual machines under Virtual Server. Normally this switch is recommended for applications requiring large amounts of memory. This switch increases the amount of user-mode virtual memory available from 2GB to 3GB; however it does this by reducing the amount of kernel-mode virtual memory from 2GB to 1GB.

Note: Unlike most applications, Virtual Server uses a good deal of kernel-mode virtual memory, so the server is most likely going to run out of kernel-mode virtual memory before running out of user-mode virtual memory.

Myth #3: Increase performance via compressed physical drives.

I recently read about a user who accidentally put his virtual machines' hard disk files onto his host server's compressed NTFS drive. He said that this gave him a performance boost of 10% to 20%.

But when I tried this on a few servers, I found that it severely impacted the performance of the guest OSes. You can try this one out to see if it works for you, but I give it a thumbs down.

Note: While Virtual Server 2005 R2 Enterprise Edition will support as many processors as its host OS (currently 32 in Windows Server 2003), and will support emulating the exact CPU that is installed on the Host (with latest service pack beta installed), the individual VMs are limited to a single logical processor and up to 3.6GB RAM. The rest of the emulated VM hardware includes the following:

About the author: Tim Fenner (MCSE, MCSA: Messaging, Network+ and A+) is a senior systems administrator who oversees a Microsoft Windows, Exchange and Office environment, as well as an independent consultant who specializes in the design, implementation and management of Windows networks.

More information on this topic:

Rate this Tip To rate tips, you must be a member of SearchWindowsServer.com. Register now to start rating these tips. Log in if you are already a member. DISCLAIMER: Our Tips Exchange is a forum for you to share technical advice and expertise with your peers and to learn from other enterprise IT professionals. TechTarget provides the infrastructure to facilitate this sharing of information. However, we cannot guarantee the accuracy or validity of the material submitted. You agree that your use of the Ask The Expert services and your reliance on any questions, answers, information or other materials received through this Web site is at your own risk.