The disadvantage is that it is impossible to know which processes are reading and writing to the disk. The iostat mentioned above only provides the overall I/O performance data of the disk. In addition to the I/O situation of each disk, the I/O situation of each process is also the focus of your attention. However, you can compare what you observe, the average request queue length or the wait time for read and write requests to complete, with the results of benchmark tests (such as through fio) to synthesize Evaluate disk saturation. In fact, there is usually no other simple way to measure saturation. You may have noticed that disk saturation is not directly available from iostat. %util is the disk I/O usage we mentioned earlier.It provides various common performance indicators such as the usage, IOPS, and throughput of each disk. iostat is the most commonly used disk I/O performance observation tool. The first thing to observe is the usage of each disk. Of course, this requires you to test the performance of different I/O sizes (usually several values between 512B and 1MB) in various scenarios such as random read, sequential read, random write, and sequential write. Generally speaking, when you select a server for an application, you must first perform a benchmark test on the I/O performance of the disk, so that you can accurately assess whether the disk performance can meet the needs of the application. In other words, when the utilization is 100%, it is still possible for the disk to accept new I/O requests. It should be noted here that utilization only considers the presence or absence of I/O, not the size of the I/O. Response time: Refers to the interval time between sending an I/O request and receiving a response.Throughput: The size of I/O requests per second.IOPS (Input/Output Per Second): Refers to the number of I/O requests per second.When saturation is 100%, the disk cannot accept new I/O requests. Excessive saturation means that the disk has a serious performance bottleneck. Saturation: Refers to how busy the disk is processing I/O.Excessive usage (such as more than 80%) usually means that there is a performance bottleneck in disk I/O. Utilization: The percentage of time the disk is processing I/O.These five indicators are the basic indicators to measure disk performance. When it comes to measuring disk performance, we often mention five common indicators: utilization, saturation, IOPS, throughput, and response time. In this article, let’s take a look at the performance indicators of the disk and how to observe these indicators. Upwards, it provides a standard interface for accessing block devices for file systems and applications downwards, it abstracts various heterogeneous disk devices into a unified block device and responds to I/O sent by the file system and applications. In my previous article: “ Linux - Disk I/O Deep Dive”, I talked about how Linux disk I/O works, and we learned that the Linux storage system I/O stack consists of the file system layer, the general block layer, and the device layer.Īmong them, the general block layer is the core of Linux disk I/O.
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