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Analyzing I/O performance in Linux

Apr 24, 2010, 07:02 (1 Talkback[s])
(Other stories by Nick Anderson)

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"Monitoring and analyzing performance is an important task for any sysadmin. Disk I/O bottlenecks can bring applications to a crawl. What is an IOP? Should I use SATA, SAS, or FC? How many spindles do I need? What RAID level should I use? Is my system read or write heavy? These are common questions for anyone embarking on an disk I/O analysis quest. Obligatory disclaimer: I do not consider myself an expert in storage or anything for that mater. This is just how I have done I/O analysis in the past. I welcome additions and corrections. I believe it's also important to note that this analysis is geared toward random operations than sequential read/write workloads.

"Let's start at the very beginning … a very good place to start. Hey it worked for Julie Andrews … So what is an IOP? An IOP is an input output (I/O) Operation and it's measured in seconds. It's good to note that IOPs are also referred to as transactions per second (tps). IOPs are important for applications that require frequent access to disk. Databases, version control systems, and mail stores all come to mind.

"Great so now that I know what an IOP is how do I calculate it? IOPS are a function of rotational speed (aka spindle speed), latency and seek time. The equation is pretty simple, 1/(seek + latency) = IOPS. Scott Lowe has a good example on his blog."

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