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IOPS refers to the number of Icano requests that can be processed by the system per unit time, usually in terms of the number of Icano requests per second, which are usually read or write data operation requests. Applications with frequent random reads and writes, such as OLTP,IOPS, are key metrics.

Data throughput (Throughput), the amount of data that can be successfully transferred per unit of time. For applications with a large number of sequential reads and writes, such as VOD (Video On Demand), more attention is paid to throughput metrics.

The time it takes for a disk to complete an Istroke O request, which consists of three parts: seek time, rotation delay and data transfer time.

The seek time Tseek is the time it takes to move the read / write head to the correct track. The shorter the seek time is, the faster the operation will be. Currently, the average seek time of the disk is generally in 3-15ms.

Rotation delay Trotation refers to the time required for disk rotation to move the sector of the requested data below the read-write head. The rotation delay depends on the speed of the disk, which is usually represented by 1x2 of the time it takes for the disk to rotate for one week. For example, a disk with an average rotation delay of 7200 rpm is about 60 million rpm, while a disk with a speed of 15000 rpm has an average rotation delay of about 2ms.

Data transfer time Ttransfer refers to the time required to complete the transmission of the requested data, which depends on the data transfer rate, which is equal to the data size divided by the data transfer rate. At present, the data transfer rate of 300MB/s interface can be achieved by IDE/ATA, which can reach 133 MB. The data transmission time of 300MB/s is usually much less than that of the first two parts of time.

Therefore, it is theoretically possible to calculate the average maximum IOPS of the disk, that is, IOPS = 1000 ms/ (Tseek + Troatation), ignoring the data transfer time. Assuming that the average physical seek time of the disk is 3ms and the disk speed is 7200, 10K and 15K rpm, the theoretical maximum of disk IOPS is

IOPS = 1000 / (3 + 6000Universe 7200Universe 2) = 140,

IOPS = 1000 / (3 + 60000 / 10000 lap 2) = 167,

IOPS = 1000 / (3 + 60000015000Universe 2) = 20000

Solid state disk (SSD) is an electronic device, which avoids the time spent on seek and rotation of traditional disks, and the memory cell addressing cost is greatly reduced, so the IOPS can be very high, up to tens of thousands or even hundreds of thousands. In the actual measurement, the IOPS value will be affected by many factors, including Icano load characteristics (read-write ratio, order and randomness, number of worker threads, queue depth, data record size), system configuration, operating system, disk drive and so on.

Therefore, when comparing and measuring disk IOPS, it must be carried out under the same test benchmark, even if there is a certain degree of random uncertainty. In general, IOPS can be subdivided into the following metrics:

Toatal IOPS, disk IOPS in the case of mixed read-write and sequential random I-IOPS O load, which is most consistent with the actual I-map O situation, and most applications pay attention to this index.

Random Read IOPS,100% randomly reads IOPS under load.

Random Write IOPS,100% randomly writes IOPS under load.

Sequential Read IOPS,100% IOPS in the case of sequential load reads.

Sequential Write IOPS,100% writes IOPS under load sequentially.

IOPS's test benchmark tools mainly include Iometer, IoZone, FIO and so on, which can be used to test disk IOPS in different situations. For the application system, it is necessary to determine the load characteristics of the data first, and then select a reasonable IOPS index for measurement and comparative analysis, so as to select the appropriate storage medium and software system.

For disk IOPS data, please refer to http://en.wikipedia.org/wiki/IOPS.

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