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Category Archives: Performance

Benchmarks – Keeping Perspective

As a performance guy, my world is full of benchmarks – both good and bad.  I wanted to share my perspective of them, as they often seem to make people crazy.

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PVSCSI and Large IO’s

Here’s a behavior that a few people have questioned me about recently:

Why is PVSCSI splitting my large guest operating system IO’s into smaller blocks?

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What is PreferHT and When To Use It

I’ve been involved recently in a couple situations in which the ‘preferHT’ advanced setting has been implemented, but for the wrong reasons. I want to re-clarify how and when it should be used. As with many advanced settings, it can be helpful or hurtful.

The Myth

“PreferHT exposes Hyper-Threading to the guest operating system” – False!

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Updated VMware Mobile Knowledge Portal

The VMware Mobile Knowledge Portal iOS and Android app has recently been updated. It sports a great new look and feel and makes finding the information you need even easier by grouping it by area in our SDDC vision.

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When to Overcommit vCPU:pCPU for Monster VMs

VMware’s conservative guidance about overcommitting your pCPU:vCPU ratio for Monster virtual machines is simple – don’t do it.

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Which vSCSI controller should I choose for performance?

I wrote a blog article in Oct 2010 on this same topic that is still frequently referenced today so I figure it was due for an update.

So what should I choose as my vSCSI controller and what are the differences between them? Continue reading

BIOS Power Policies Affect Performance

How should one set the BIOS power management policies of their VMware infrastructure for maximum virtual performance?

Simple: OS Controlled in the host BIOS, Balanced within vSphere

But are there exceptions?

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Microsoft Operating System Time Sources and Virtual Hardware 10

More recent versions of Microsoft operating systems contain the ability to detect if they are running virtualized or not.  This is accomplished through the checking of a CPUID hypervisor-present bit presented by the VMware virtual hardware.  Since virtual hardware 7, VMware has implemented this interface, which is required by the Microsoft SVVP program.

FACT: Did you know VMware ESX 3.5u2 was the world’s first hypervisor to be qualified under the Microsoft SVVP program?

However, as Microsoft continues to change and update its specifications, lets look at a specific behavior in which virtual machine performance can be impacted by the operating system accessing a time source inefficiently. Continue reading

Understanding vSphere Active Memory

We’ve all seen “Active” memory reported within various vSphere interfaces, but how many us really know what it describes.  I think you might be surprised.

Let’s look at its definition to get us started:

Active Memory - ”Amount of memory that is actively used, as estimated by VMkernel based on recently touched memory pages.”

There are some very important details we need to breakdown here.  Example: What is it used for? What does estimated mean?  How do we define recently? Continue reading

vSphere Replication 5.5 Performance Findings

A few days ago I did a post on why VR is much quicker with version 5.5 than it had been in the past.

Now let’s take a look at what the result of those changes is.

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