At present, hard disks can be divided into IDE hard disks and SCSI hard disks in terms of interfaces (at present, some products still support PCMCIA interface, IEEE 1394 interface, SATA interface, USB interface and FC-Al interface, but relatively few); IDE hard disk is our daily hard disk. Because of its low price and poor performance, it has been widely used in PC.
At present, most of the hard disks used by personal computers are of this type. Another kind of hard disk is SCSI hard disk (SCSI is a small computer system interface). This kind of hard disk product is widely used in servers because of its good performance, but at the same time it is expensive, so SCSI is not often seen on ordinary PCs.
Compared with the hard disk of ordinary PC, the hard disk used on the server has the following four characteristics.
1, come on
The hard disk used by the server is fast, which can reach 7200 or 10000 rpm or even higher; A large write-back cache (generally 2MB or 4 MB) is also configured; The average access time is relatively short; The external transfer rate and internal transfer rate are higher. Standard SCSI hard disks such as ultra-wide SCSI, ultra-2 wide SCSI, Ultra 160 SCSI and Ultra320 SCSI are adopted, and the data transmission rate per second can reach 40MB, 80MB, 160MB and 320MB respectively.
2, high reliability
Because the server hard disk runs almost 24 hours a day, it bears a huge workload. It can be said that if there is something wrong with the hard disk, the consequences will be unimaginable. Therefore, the current hard disks all adopt S.M.A.R.T technology (self-monitoring, analysis and reporting technology), and hard disk manufacturers all adopt their own unique advanced technology to ensure data security. In order to avoid unexpected losses, the server hard disk can generally withstand the impact of 300G to1000 g.
3. Use SCSI interface more.
Most servers use SCSI hard disks, which have high data throughput and extremely low CPU utilization. SCSI hard disk can only be used through SCSI interface. Some server motherboards have integrated SCSI interfaces, and some have special SCSI interface cards. A SCSI interface card can connect seven SCSI devices, which is incomparable to IDE interface.
4, can support hot plug.
Hot plug is a hard disk installation method supported by some servers, which can pull out or insert the hard disk without stopping the server, and the operating system automatically recognizes the change of the hard disk. This technology is very necessary for a 24-hour server.
When we measure the performance of a server hard disk, we should mainly refer to the following indicators:
Spindle speed
Among all the indexes of hard disk except capacity, spindle speed is the most noticeable performance parameter, and it is also the first decisive factor to determine the internal transmission speed and continuous transmission speed of hard disk. At present, the speed of hard disk is mostly 5400 rpm, 7200 rpm, 10000 rpm, 15000 rpm. Judging from the current situation, SCSI hard disk with 10000rpm has the advantage of high cost performance and is the mainstream of hard disk at present, while hard disks with 7200rpm and below are gradually fading out of the hard disk market.
Internal transmission rate
The internal transmission rate is the decisive factor to evaluate the overall performance of hard disk. Hard disk data transfer rate is divided into internal transfer rate and external transfer rate; Usually, the external transmission rate is also called Burstdata transmission rate or interface transmission rate, which refers to the speed of outputting data from the cache of the hard disk.
At present, the external transmission rate of Ultra 160 SCSI technology has reached160 MB/s; The internal transfer rate, also known as the maximum or minimum continuous transfer rate, refers to the speed at which the hard disk reads and writes data on the disk. At present, most mainstream hard disks are between 30MB/s and 60 MB/s. Because the internal transmission rate of hard disks is less than the external transmission rate, only the internal transmission rate can be used as a real standard to measure the performance of hard disks.