A few summary of disk performance

We know that the current drive can be divided into single disc and multi- disc, a single disc only one disc, and multi-disc disc has multiple discs, each of the two sides of the disc can be stored data , and each disk face requires a read and write head . However, for a disk, at the same moment, there can be only one head to read and write to the disk, regardless of the disk body has a few discs , therefore, increase the disk does not increase the concurrent IO capability, only increase the storage capacity of the disk.

In fact, for a disk, there are two ways to increase storage capacity:1, increase the disc, 2, increase the density of each disc . In addition, if the same disk, if more than one head can work concurrently, you can provide similar RAID-like concurrent read and write capability.

Determine the read and write performance of a hard disk The main is that this does not include SSDs and other new hard drives.
First, Seek time
Seek time refers to the time required for the head machine to move to the corresponding cylinder , since the disk random IO needs to move the head frequently to seek the path, therefore, seek time is a primary factor that affects the disk random IO. The head needs to change the cylinder or the track frequently, and the time for data transmission is much more than the former. Therefore, if you can increase the seek time of the head, you can increase the disk random ioPS. The current disk seek time is generally within 10ms , such as the Seagate HDD Random read seek time at 3.5MS, the random write seek time is 4ms.

Second, the disc speed
As a result of continuous Io, the head is basically on the same cylinder from the head 1 to the head n for continuous IO operation, each head in the track of all sectors of the data operation is completed before the next head operation, therefore, in this case, the speed is the primary factor affecting the performance of disk continuous IO. In the case of continuous IO, speed is a primary factor in increasing the IOPS of continuous IO because of the small number of disk changes to the track or cylinder. The current hard drive speed can basically be 10000-15000 rpm.

Third, the density of the disc

This is easier to understand, in the search time and the speed of the disc, the disk density of higher disks, unit space storage capacity more, that is, the data density is greater, in unit time, can read or write the amount of data more.

Four, interface speed

Interface speed is generally much larger than the disk itself read and write speed, so for a disk, the interface speed is not called the real bottleneck. At present, the IED interface of the hard disk, the IED essence is PATA interface specification, the current ATA-7, also known as ATA133 interface speed can reach 133m/s, and SATA specification of 2.0, you can reach 300m/s.

A few summary of disk performance