Defining measures

What is an IOPS Really?

Measuring IOPS

Several tools are commonly used for measuring read/write IOPS on systems. The first one I want to mention is Iometer [9], which you commonly see used on Windows systems. The one I most commonly use is Iozone [10], an open source, easy to build and use tool that has a number of test options and even allows you to vary the data "compressibility" for I/O function payloads.

Another common tool for testing read/write IOPS is fio [11], which lets you run a wide variety of tests, including mixing read and write IOPS.

The last tool I want mention is IOR [12], which is commonly used in testing parallel storage solutions often found in HPC. It is also used as part of the IO500 [13] list. You can use it to test really large amounts of I/O and vary the I/O function payload size, as well as either read or write operations.


IOPS is an important and often used I/O performance test. It can be very useful because many applications use very small I/O payloads and executing them quickly improves application performance. However, although the storage world has sort of created a definition that is vague and ripe for abuse, there is no standard definition of an IOPS.

In this article, I hope I have explained what an IOPS is and what goes into its definition. Parameters such as the type, function payload size, and pattern of I/O operations, as well as the operating system I/O scheduler and queue depth, are critical when reporting and understanding IOPS results.

The Author

Jeff Layton has been in the HPC business for almost 25 years (starting when he was 4 years old). He can be found lounging around at a nearby Frys enjoying the coffee and waiting for sales.

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