Test storage system performance with Iometer

Scott Lowe takes you step-by-step through the process of installing and running Iometer, an open source tool that you can use to test the performance of your storage solution.

When implementing storage of any kind, whether it's directly attached to a server, connected to your network (NAS), or on its own network (SAN—Fibre Channel or iSCSI), it's important to know just how well your storage performs. If you can't pinpoint this information, growth is difficult since you can't properly manage it. Iometer, an open source tool, available for download from, can help you identify this critical infrastructure measure and help you make better decisions about what kind of storage you need or whether your current storage solution can handle an increased load.

Iometer actually serves an additional purpose beyond just measuring I/O performance—it can also generate the workload that is used to test the system (this component is called Dynamo). It can be configured in a number of ways that allow very granular testing to take place so that it can test multiple scenarios. The Dynamo component must be installed on each system for which you would like to gather performance results. Iometer and Dynamo can be installed on the same system in cases where you want to test the performance of the local disk system.

Installing and running Iometer and Dynamo

The Iometer installation under Windows couldn't be any easier. Simply double-click the downloaded file and accept all of the default options. This installs Iometer onto your system and places a shortcut on your Start Menu.

Iometer is extraordinarily versatile, and I don't have room in this article to go over every option (The Users Guide is more than 80 pages long). However, I will go over some basic configurations and explain how to run tests locally.

For a local test, just start Iometer on the machine to which you installed the program. In Figure A below, see the Topology section at the left. In that section you see BASE2K3, which is the name of the machine (also called a "manager" in Iometer-speak) on which Iometer is running, and Worker 1. A worker is an individual thread run by Dynamo (which is started automatically when you run Iometer). At the right, the default tab is the Disk Targets tab, which lists the drives that are available to use for tests.

Figure A

Iometer main window – disk targets

For any Iometer test, you must select access specifications from the Access Specifications tab in Figure B. The information on this tab specifies the type of IO operations that will be performed by Iometer, allowing you to customize tests for your particular application. This example runs tests with 512-byte and 32-KB chunks of data, with read frequency assumptions of 50 percent and 25 percent, respectively. You can customize these assumptions by clicking the New or Edit buttons and creating your own.

Figure B

Access specifications control exactly how tests run

Before you run your test, you can also change other parameters, such as the length of the test. For example, if you want to get a true average reading of your disk system performance, you might want to run the test for hours instead of seconds to guard against running the test at the same time a user is pulling a large file from the system. Many test parameters can be adjusted by using the Test Setup tab, shown below in Figure C.

Figure C

The test setup tab provides a place to change overall test parameters

Once you configure your test, click the green flag on the menu bar to start things running. Click the Results Display tab to get a real-time view of your running test. A sample results display is shown below in Figure D. You can expand a particular result into its own screen by pressing the right-arrow at the right of each test, which results in a screen similar to the one shown in Figure E.

Figure D

The Result Display tab provides quick access to a lot of information

Figure E

Drill down into individual results

This tip is intended to be a very basic introduction to Iometer, a tool that can help you get a measure for your storage system's performance.

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