The protocol of the hard disk box actually refers to what protocol the hard disk box supports. Generally, the protocol of the hard disk box is the same as the hard disk protocol. It is mainly divided into two types: interface protocol and transmission protocol:
1. Interface protocol
Interface protocol, which is the main classification method of SSD hard disk, is usually classified according to the interface into SATA, SATA-E, mSATA, M.2, U.2, PCI-E, Macbook dedicated interface, etc., among which it is the most widely used. They are SATA, mSATA, M.2, and PCI-E. In fact, strictly speaking, there are only two types: SATA and PCI-E, because mSATA also uses the SATA protocol, just because the interface is a mini version. M.2 is divided into SATA and PCI-E, so it is actually a competition between SATA and PCI-E.
2. Transmission protocol
There are two main types of transmission protocols:
(1)AHIC transmission protocol
AHCI (Serial ATA Advanced Host Controller Interface) Serial ATA Advanced Host Controller Interface/Advanced Host Controller Interface is used to replace the previous generation IDE. Essentially, they are all based on the design of mechanical hard disks, so they have been gradually eliminated. The current mainstream SSD products must turn on the AHCI mode in the BIOS settings before installation to maximize performance. Many users have installed SSD products. It was found that the speed was only 300MB/s and less than 400, mostly because the AHCI mode was not turned on.
The SATA interface and AHCI standard currently used are actually designed for high-latency mechanical hard disks. Currently, mainstream SSDs still continue to use them. In the early days, when the performance of SSDs was not high, you may not think there was any problem. However, as the performance of SSDs gradually increases, These standards have become a major bottleneck restricting SSDs. The AHCI standard designed for mechanical hard drives is not very suitable for low-latency SSDs.
(2) NVMe transmission protocol
NVMe (Non-Volatile Memory express) is a protocol similar to AHCI based on the M.2 interface. It is a protocol specially designed for flash storage. It is because everyone found that the AHCI standard is not suitable for low-latency SSD products, so in order to liberate the performance of SSD, a new storage specification standard was re-formulated. Using PCI-E channel, current high-speed SSD products must support the NVMe protocol. , and the speed is generally above 2000MB/s, and those with excellent performance can easily exceed 3000MB/s.
NVMe is actually a logical device interface standard like AHCI. Unlike AHCI, NVMe is a specification for SSDs that use PCI-E channels. From the beginning, NVMe was designed to take full advantage of the low latency and parallelism of PCI-E SSDs, as well as the parallelism of contemporary processors, platforms, and applications. sex. The parallelism of SSD can be fully utilized by the host hardware and software. Compared with the current AHCI standard, the NVMe standard can bring performance improvements in many aspects.
One of the advantages of NVMe is low latency. This is mainly due to the streamlined storage stack, which allows NVMe to issue commands without reading registers. Each command of AHCI requires reading 4 non-cacheable registers, resulting in approximately 2.5μs of additional latency. The advantage of low latency and good parallelism is that the random performance of SSD can be greatly improved, and it can achieve excellent speed at any queue depth.