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 www.iometer.org, 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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