hard Disk Interface
The current hard disk interface type is not much, mainly IDE, SCSI, SATA three kinds. Many times the IDE replaces the Ultra ATA, many people are accustomed to the Ultra ATA hard disk is called IDE hard disk, but need to explain that the concept of the IDE is greater than ata--in principle all hard drive integrated controller design belongs to IDE,SCSI is no exception. Of course, with the IDE referring to ATA has become a lot of inertia, SATA began to distinguish between the IDE and ATA. Mature inexpensive is the IDE, the most emerging is SATA, stable price high SCSI. The first occurrence was the IDE interface, which later appeared as a SCSI interface, primarily for the server. If you look closely, you can find that recently the computer industry's system bus is the development of the serial, hard disk interface Bus SATA is a representative, including the future will replace the AGP interface of the graphical interface standard pci-express, are moving towards the serial direction.
1. IDE Interface: (Hint: xseries owns only one by one 120GB IDE hard disk)
The IDE's English is all called: Integrated Drive Electronics, is currently the most mainstream hard disk interface, including the main interface of optical storage class. It has become mature, cheap and stable after several years of development. The IDE interface uses a flat cable of 40 or 80 cores to connect the hard drive to the motherboard, with a maximum of 2 IDE devices (hard drives or light storage) attached to each line. The early use of IDE multi-function cards plugged into the motherboard, and then connected to the IDE line, this function card has been eliminated; the motherboard currently offers 2 IDE interfaces, which are inexpensive and easy to install compared to the IDE multifunction card. The IDE interface is also divided into udma/33,udma/66,udma/100,udma/133. At the end of 1996, Quentin and Intel announced the joint development of the Ultra Dma/33 New Eide interface, because of its data transmission rate of 33mb/s, it is called UDMA/33, the following udma/66,udma/100,udma/133 named Ditto. Ultra DMA uses the rising and descending edges of the clock pulses to be used as the pass-through signal, that is, to transmit data once per half clock cycle, which multiplies the maximum external transfer rate from 16.6mb/s to 33.3mb/s. In addition, Ultra DMA using bus control, the hard disk has a direct memory channel controller, can greatly reduce the hard disk in reading and writing CPU occupancy rate, the CPU occupancy rate from 92% to 52%, which is also an important role of Ultra DMA. Of course, to implement Ultra DMA functionality, motherboards and corresponding drivers that support the Ultra DMA specification are also required. All IDE hard disk connectors use the same 40-pin connector, as shown in the following illustration:
2.SCSI interface (hint: xseries has all SCSI hard drives of the industry specifications)
SCSI English full name: Small Computer System Interface, it occurs mainly because the original IDE interface's hard disk speed is too slow, the transfer rate is too low, so the high-speed SCSI hard drive appears. In fact, SCSI is not designed for the hard disk, in fact it is a total line interface. Because it works independently of the system bus, so its biggest advantage is that its system occupancy rate is very low, but the speed, high transmission rate of SCSI interface hard disk also has its shortcomings: high prices, installation inconvenience, but also need to set up and install the driver, so this interface hard disk is mostly used for high-end applications such as servers. It is the use of a 50-core flat cable, RPM above, but with the development of IDE technology, now the IDE interface of the hard disk in capacity and speed with the SCSI interface hard disk, and in the near future, it may not exist. All SCSI interfaces use 1 of the following 3 types of connectors, as shown in the following illustration:
3.SATA interface (hint: xseries has 80GB and 160GB two SATA hard drives)
Sata's English full name is: Serial-ata (serial), the IDE series belong to Parallel-ata (parallel), SATA is recently promulgated the new standard, with faster external interface transmission speed, data calibration measures more perfect, the initial transmission rate has reached the 150mb/s, Higher than the highest udma/133 of the IDE. Because of the use of lines to interfere with the smaller serial lines between the signal transmission, so compared to the original parallel bus, Sata's working frequency greatly improved. Although the bus bit width is small, the SATA 1.0 standard can still reach 150mb/s, the future SATA 2.0/3.0 can be increased to 300 to 600mb/s. And S-ata has a more concise and convenient layout wiring, in the limited chassis, more conducive to cooling, and simple connection, so that the internal electromagnetic interference to reduce a lot. Believe that the last is SATA interface, SCSI and IDE interface hard drives will be used in the future SATA interface standards. We know that the SATA interface is incompatible with the IDE hard disk interface and the power supply interface is not the same, the following image is compared with the parallel ATA transmission line:
The left is a serial data transmission line, the right side is a parallel data transmission line
The input interface of the power supply is also different from the original 4pin power supply and needs to be converted.
ATA includes PATA (Parallel ata, Parallel ATA) and SATA (Serial ATA, Serial ATA).
PATA is the IDE above.
SATA has SATA1, SATA2, SATA3 three generations, transmission speed is divided into 1.5G, 3G, 6G. The shape of the three-generation SATA is the same as the following
Looking at three kinds of hard disk interface, PATA is gradually replaced by SATA is inevitable trend, the rest is only a matter of time. And SCSI because of its own advantages, I am afraid the status of a time difficult to waver. SCSI advocates are also starting to develop serial SCSI standards, and perhaps the complete replacement of SCSI connectors by serial SCSI is the real trend.
There are now two main hard disk interface technologies on the server, SATA and SCSI, and the products that use SAS hard drives are currently listed, and of course high-end optical drives, the first two of which are the most common. Here we have a brief introduction to SATA, SCSI, SAS and other interface technologies.
SATA
SATA (serial Advanced Technology attachment) is the abbreviation for Serial ATA, which is currently available SATA-1 and SATA-2 two standards, the corresponding transmission speed is 150mb/s and 300mb/s. SATA is primarily used for PATA interface technology that has replaced bottlenecks. From the speed of this point, SATA in the transmission mode SATA is also more advanced than Pata, has been far away from the PATA hard drive behind. Second, from the data transmission point of view, Sata than Pata anti-interference ability.
SATA-1 has been widely used, its maximum data transmission rate of 150MBPS, signal line up to 1 meters long. SATA is generally a point-to-point connection, that is, a SATA interface connected to the motherboard, the other end directly connected to the hard drive, no other device can share this data line, and parallel ATA allows this (each data cable can connect 1-2 devices), There is therefore no need to set the master and the disk as parallel ATA hard drives.
In addition, SATA has the hot plug function is not comparable to PATA, the use of this feature can be more convenient to build a disk array. Serial data lines due to only the use of four-pin structure, so compared with the mouth installed more convenient, more conducive to reducing the cable in the chassis, conducive to heat dissipation.
SCSI
SCSI (Small Computer system Interface) is a kind of storage cell interface model specially designed for small computer system, which can carry out dynamic division of work for multiple devices in the computer, and can be easily distributed and completed dynamically for multiple tasks required by the system.
The SCSI specification has grown to today and is the sixth generation technology, from SCSI (8bit), Wide scsi (8bit), Ultra Wide scsi (8bit/16bit), Ultra Wide SCSI 2 (16bit), Ultra 160 scsi (16bit) to today's ultra-1.2mb/s SCSI, the speed from the 320mb/s has a qualitative leap in the current. The ultra-320mb/s SCSI interface is used by the current mainstream SCSI hard drives to provide the transfer speed of the interface.
SCSI hard disks also have a SCA2 interface (80-pin) that specifically supports hot-plug technology, which can be easily plugged in by using the SCSI backplane. Hot-swappable features are now almost essential in workgroup and departmental servers.
Summary:
Because SCSI has low CPU usage, multitasking, high efficiency, many connection devices, long connection distance and other advantages, for most server applications, SCSI hard drives are recommended and the latest ULTRA320 SCSI controller is adopted; SATA drives also have hot-swappable capabilities and can be well scalable on the interface, such as using Scsi-sata, Fc-sata conversion interfaces, and SATA port multiplier in a rack-top server to provide better flexibility than SCSI. For low-end small server applications, you can use the latest SATA hard drives and controllers.
After determining the interface and type of the hard disk, we should focus on the above mentioned technical indicators affecting the performance of the hard disk, according to the speed, single disk capacity, average seek time, caching and other factors, and combined with capital budget, select the most appropriate cost-effective hard drive program
