The Essentials Series: Tactics in Optimizing Virtual Machine Disk IOPS

by Greg Shields


During virtualization's early years, IT focused on processor utilization as a primary bottleneck.  Today, the experts realize that disk I/O has a far greater impact than ever before realized.  You probably know that virtual machine performance will suffer when hardware doesn't supply enough disk IOPS.  But were you aware that VM and virtual environment configurations can have an impact as well?

In The Essentials Series: Tactics in Optimizing Virtual Machine Disk IOPS, author and IT expert Greg Shields shows you how a bad design combined with incorrect VM configurations can be deleterious on performance.  You'll understand the poor practices that hinder VM disk I/O and how Windows old enemy fragmentation has a significant impact.  Optimizing your VMs requires doing the same with their disks.  That's why this ES concludes with a look at the requirements you'll want in your specification for a VM disk optimization solution.


Article 1: Poor Practices that Hinder VM Disk IOPS

Spend time in enough IT shops, and you'll eventually discover that the same mistakes are made everywhere. At least that's the feeling I get when pondering all the virtual environments I've seen in my consulting travels. From large to small, simplistic to highly advanced, you'd be surprised how often the same poor practices are incorporated into people's designs.

Most interesting about those mistakes, particularly in the case of virtual machine (VM) performance, is how unnoticed they often go. IT shops with heavy‐duty hardware experience the classic signs of poor performance and often don't even realize it. Others might realize performance isn't to par but focus troubleshooting attentions on entirely the wrong things, such as resources like processing and memory that comprise virtual environments, incorrect configurations, or omitting key technologies the lack of which creates big problems down the road.

Your storage represents one of those oft‐forgotten areas where poor VM performance can come from. Too often, storage itself is thought of only in terms of capacity: "I have fifteen terabytes of storage I can provision to virtual machines." Yet today's storage and the demands we put on it requires a second metric that's just as important: performance.

Input/Output Operations per Second (IOPS) is a common measurement for quantifying storage performance. In general terms, a unit of IOPS represents how many "things" a storage device can accomplish in a given unit of time. Those things might be reading from a disk or writing to it, deleting data from it, or performing storage maintenance tasks.

The amount of IOPS you have to work with—your supply—is greatly driven by your design. Incorporate faster disks, more storage processors, or a wider connection bandwidth, and you'll see IOPS go up. It is also driven by the collection of decisions you've made in configuring hosts and VMs. Overload your connections, ask too much of your disk spindles, or configure VMs in ways that require more‐than‐necessary storage attention, and you'll quickly find that IOPS suffers. And when IOPS suffers, so do your VMs.

In my travels, I've seen plenty of poor storage practices. They're laid into place by wellmeaning administrators who simply forget that storage performance is as important as storage capacity. Let me share a few of my favorite stories from those travels. In the telling, hopefully you'll learn to avoid common poor practices that hinder VM disk IOPS.

Article 2: The Impact of Fragmentation on VM Disk IOPS

Virtualization's early years found many an administrator focusing attention on processor utilization as primary bottleneck. "Insufficient processing power," we thought back then, "creates a shortfall condition. That shortfall translates directly to poor performance."

Those assumptions weren't necessarily incorrect. Lacking processing power, you will experience performance issues. Today, however, we realize that disk I/O has a far greater impact than ever before realized. You probably know that VM performance suffers when hardware doesn't supply enough disk IOPS, or when VMs demand too much. But were you aware that VM and virtual environment configurations can have an impact as well? One critically‐important facet of the overall configuration story centers around disk fragmentation's impacts on IOPS.

Article 3: Defining Requirements for a VM Disk Optimization Solution

This series has highlighted the design tactics for best optimizing VM disk IOPS. Following the principles presented in the first two articles will ensure your hardware best meets the demands of your VMs. This series has also explored the specific issue of fragmentation that exists irrespective of how your design is ultimately constructed. Getting to maximum IOPS for VMs requires seeking that best design. It also requires a careful look at the configurations you apply to VMs and virtual hosts so that their activities don't foment poor performance. Fragmentation and its elimination are components of those configurations. More importantly, however, is the recognition that solutions for disk optimization may be a necessary part of your overall design.

Disk optimization, particularly with virtual environments, is more than just defragmentation. Performing disk optimization correctly also requires optimizing free space—those proverbial "holes" inside disks. It requires fragmentation prevention, stopping the problem before it happens. It also demands an orchestration of activities across host and collocated VMs, ensuring that optimization activities themselves don't become an impact on performance. As you look towards options for disk optimization, consider the following four important requirements as your specifications for a virtualization‐friendly solution.