Concept of disk IOPS and calculation of IOPS

The concept of disk IOPS and the concept of IOPS (Input/Output Per Second) is the Input Output Per Second (or read/write count), is one of the main indicators to measure disk performance. IOPS refers to the number of I/O requests that the system can process per second, i/O requests are generally read or write data operation requests. For applications with frequent random reads and writes, such as OLTP (Online Transaction Processing), IOPS is a key indicator. Another important metric is Throughput, which refers to the number of data records that can be successfully transferred per unit time. For a large number of sequential read/write applications, such as Video editing On TV stations and Video On Demand VOD (Video On Demand), more attention is paid to throughput indicators. The IOPS Calculation Method of www.2cto.com is essentially a mechanical device on a traditional disk, such as FC, SAS, and SATA disks. The speed usually ranges from 5400/7200/10 K/15 K rpm. The key factor affecting the disk is the disk service time, that is, the time it takes for the disk to complete an I/O request. It consists of three parts: Seeking time, rotation delay, and data transmission time. Seek time Tseek refers to the time required to move the read/write head to the correct track. The shorter the tracing time, the faster I/O operations are. Currently, the average tracing time of a disk is generally 3-15 ms. The rotation delay Trotation refers to the time required to rotate the disk to move the sector where the request data is located to the bottom of the read/write head. The rotation delay depends on the disk speed, which is usually expressed by 1/2 of the time required for disk rotation for one week. For example, the average rotation latency of a 7200 rpm disk is about 60*1000/7200/2 = 4.17 ms, while the average rotation latency of a 15000 rpm disk is about 2 ms. Data transmission time Ttransfer refers to the time required to complete the data requested for transmission. It depends on the data transmission rate, and its value is equal to the data size divided by the data transmission rate. At present, IDE/ATA can reach 133 MB/s, and sata ii can reach the interface data transmission rate of 300 MB/s. The data transmission time is usually far earlier than the first two parts. Therefore, theoretically the maximum IOPS of the disk can be calculated, that is, IOPS = 1000 MS/(Tseek + Troatation), ignoring the data transfer time. Assuming that the average physical tracing time of a disk is 3 ms and the disk speed is 1000, 10 K, and 15 K rpm, the theoretical maximum IOPS of the disk is www.2cto.com IOPS = 60000/7200/(3 +/2) = 140 IOPS = 1000/(3 + 60000/10000/2) = 167 IOPS = 1000/(3 + 60000/15000/2) = 200 solid state ssd is an electronic device, this avoids the time spent on searching and rotating traditional disks, and greatly reduces the overhead of storage unit addressing. Therefore, IOPS can be very high and reach tens of thousands or even hundreds of thousands. In actual measurement, IOPS values are affected by many factors, including I/O load characteristics (read/write ratio, order and random, number of working threads, queue depth, and data record size), system configuration, operating system, disk drive, and so on. Therefore, when comparing the IOPS of a disk, it must be performed under the same test benchmark, even if it produces random uncertainty. In general, IOPS can be subdivided into the following indicators: Toatal IOPS, disk IOPS under mixed read/write and sequential random I/O load, which is the most consistent with the actual I/O situation, most applications focus on this metric. Random Read IOPS: IOPS in the case of 100% Random Read loads. Random Write IOPS: IOPS under 100% Random Write loads. Sequential Read IOPS: IOPS in the case of 100% Sequential load reads. Sequential Write IOPS: The IOPS under 100% Sequential Write loads. IOPS testing benchmark tools include Iometer, IoZone, and FIO, which can be used to test disk IOPS in different situations. For an application system, you must first determine the load characteristics of the data, then select appropriate IOPS indicators for measurement and comparative analysis, and then select the appropriate storage medium and software system.