Differences between hard disk SCSI (SAS), IDE, and SATA

 

Hard Disks include SSD, HDD, and HHD. SSD uses flash memory particles for storage, HDD uses magnetic discs for storage, and hybrid hard disks (HHD: hybrid hard disk) is a hard disk that integrates the magnetic hard disk and flash memory.

HDD: hard disk drive is one of the main storage media of a computer. It consists of one or more aluminum or glass-based discs. These discs are covered with magnetic materials. The vast majority of hard disks are fixed and permanently sealed and fixed in the hard drive.

SSD: solid state disk (solid state disk) is a hard disk made from an array of Solid State electronic storage chips.

Hard DiskData interfaces are generally divided into ATA and SATA (see the IDE Interface) as well as SCSI and SAS.

A scsi hard disk is a hard disk that uses the SCSI interface. It is widely used on servers because of its good performance and high stability. At the same time, it is expensive because it is expensive, so it is rarely seen in ordinary PCs.

The SCSI interface must be mentioned when it comes to SCSI hard disks. scsi is short for the small computer system interface (Small Computer System Interface). It uses the 50-pin interface and looks similar to the ordinary hard disk interface. The SCSI hard disk has many advantages over the ordinary IDE Hard Disk: The interface speed is fast, and because it is mainly used for servers, the hard disk performance is also relatively high, the hard disk speed is fast, the cache capacity is large, low CPU usage, far better scalability than IDE hard disk, and supports hot swapping.

Currently, SCSI hard drives are mainly manufactured by Seagate, quantum, IBM, and WD ). SCSI hard disks are more expensive. SCSI hard disks of the same capacity are more than 80% more expensive than IDE hard disks. Therefore, SCSI hard disks are mainly used for medium and high-end servers and high-end workstations.

To enable the hard disk to adapt to the working environment with large data volumes and ultra-long working hours, servers generally adopt high-speed, stable, and secure SCSI hard disks.

The current hard disk from the interface, can be divided into IDE hard disk and SCSI hard disk (there are some support PCMCIA Interface, ieee1394 interface, SATA interface, USB interface and FC-AL (Fiber Channel-arbitrated loop) fiber Channel Interface products, but relatively few); IDE is the hard disk we use in daily use. It is widely used in PCs because of its low price and poor performance. However, Sata has gradually replaced the IDE hard drive and become the mainstream in the PC market.

At present, the vast majority of hard disks used on PCs are of this type. Another type of hard disk is the SCSI hard disk (SCSI is the interface of the small computer system interface). Because of its good performance, such hard disk products are widely used on servers, but at the same time, it is expensive, so SCSI is not often seen on ordinary PCs.

Compared with hard disks of ordinary PCs, the hard disks used on servers have the following four features.

1. Fast

The server uses a hard disk with a high speed, which can reach 7200 or 10000 RPM, or even higher. It is also configured with a large (generally 2 MB or 4 MB) Write-back cache; the average access time is short. The external transmission rate and internal transmission rate are higher. standard SCSI hard disks such as ultra wide SCSI, ultra2 wide SCSI, ultra160 SCSI, and ultra320 SCSI are used, the data transmission rate per second can reach 40 MB, 80 Mb, 160 MB, and 320 MB respectively.

2. High Reliability

Because the server's hard drive runs around 24 hours a day, it bears a huge workload. It can be said that if there is a problem with the hard disk, the consequences will be unimaginable. Therefore, the current hard drive uses S. m.a. r. T Technology (self-monitoring, analysis, and reporting technology), while hard drive manufacturers use their own advanced technology to ensure data security. In order to avoid unexpected losses, the server hard disk can withstand the impact of GB to GB.

3. multiple SCSI Interfaces

Most servers use SCSI hard disks with high data throughput and extremely low CPU usage. The SCSI hard disk can be used only through the SCSI interface. Some Server Boards integrate the SCSI interface, some have dedicated SCSI interface cards, and one SCSI interface card can be connected to seven SCSI devices, this is incomparable to ide interfaces.

4. Supports hot swapping

Hot Swap is a hard disk installation method supported by some servers. You can unplug or insert a hard disk without stopping the server. The operating system automatically identifies hard disk changes. This technology is essential for a 24-hour uninterrupted server.

When measuring the performance of a server hard disk, we should refer to the following indicators:

Spindle Speed

In addition to capacity, the spindle speed is the most notable performance parameter among all indicators of the hard disk. It is also the first factor that determines the internal transmission speed and continuous transmission speed of the hard disk. Today, the hard drive speed is mostly 5400 rpm, 7200 RPM, 10000rpm rpm, and 15000 rpm. From the current situation, 10000rpm of SCSI hard disks have the advantage of high cost performance and are currently the mainstream hard disks, while 7200rpm and below are gradually fading out of the hard disk market.

Internal Transfer Rate

The internal transmission rate is the decisive factor for evaluating the overall performance of a hard disk. The hard disk data transmission rate is divided into internal and external transmission rate. The external transfer rate is also the burstdata transfer rate or interface transfer rate, which refers to the speed at which data is output from the hard disk cache.

At present, the external transmission rate using ultra 160 SCSI technology has reached 160 Mb/s; the internal transmission rate is also called the maximum or minimum continuous transmission rate (sustained transfer rate ), it refers to the speed at which disks read and write data on disks. Most mainstream hard disks are between 30 Mb/s and 60 Mb/s. Because the internal transmission rate of the hard disk is smaller than the external transmission rate, only the internal transmission rate can be used as a real standard to measure the performance of the hard disk.