What are SCSI and RAID controllers

Introduction of SCSI Card

The English of SCSI is all called "Small Computer system Interface", Chinese name "Small computer system interface". It is a peripheral interface, in the server is mainly used by the hard disk, in addition, there are cd/dvd-rom, CD-R/RW, scanners, tape drives, etc. also have the use of this interface. In fact, SCSI is not a new type of interface, as early as the 1986 SCSI standards have been set up, has also been going through nearly 20 years of time. Early Apple Inc. took the lead in selecting SCSI as the standard interface for Macs computers, with many peripherals connecting to the main system with this unified interface. In the case of PCs, SCSI cards and devices are expensive, and almost every peripheral has a cheaper interface to replace, which is not favored, although performance is far less than the SCSI interface and there are not many SCSI devices available at the time. But now, support SCSI interface Peripherals products from the original only hard drive, tape drive two, add to scanners, optical drives, burners, MO and other devices, the opportunity to contact SCSI is gradually increasing, coupled with the progress of manufacturing technology, SCSI card and peripheral prices are no longer high, Display SCSI market is already quite mature.

SCSI interfaces have always been known for high transmission rates and high reliability, and are widely used in servers and high-end PCs, which we often refer to as hard drives that have SCSI interfaces. SCSI itself is also constantly improving the development of its application speed from the initial 4mb/s has been developed to the current fastest 320mb/s, but also upward development. Compared to the commonly used IDE (ATA) interface in PC (currently the fastest 133mb/s), its transmission rate has obvious advantages, so in the server is usually a SCSI interface of the hard disk, rather than the common IDE interface hard disk. However, the current transmission rate of the new SATA (Serial IDE) interface is also near the SCSI interface rate and is being applied in the server.

In addition to the IDE interface, the SCSI interface also solves the problem of multiple device hooks, besides having the advantage of transmission rate. The IDE interface for common PC boards supports only 4 IDE devices, but 1 SCSI interfaces can hook up 15 devices, which is a significant advantage for servers that require a mass storage system. Of course, the advantages of SCSI interface is much more than this, specifically no longer detailed.

SCSI technology has developed so far that there are quite a few types of SCSI controllers available.

The main types and their performance characteristics are as follows:

(1) SCSI-1: It was the earliest SCSI interface, developed in 1979 by Shugart (the predecessor of Seagate), and was recognized by the United States Standard Agreement in 1986 Sasi (Shugart Associates System Interface, Schgatt Joint System interface). It features synchronous and asynchronous SCSI peripherals that support 7 8-bit peripherals with a maximum data transfer rate of 5mb/s and support for worm peripherals.

(2) SCSI-2: It is the SCSI-1 follow-up interface, which was proposed in 1992, also known as Fast SCSI. If the original 8-bit parallel data transmission is referred to as "Fast SCSI", its data transmission rate is 10mb/s, the maximum number of support connected devices to 7 units. Later, the use of a 16-bit parallel data transfer mode, "Fast Wide SCSI", its data transmission rate increased to 20mb/s, the maximum number of support connected devices to 15 units.

(3) SCSI-3: It is the "Ultra SCSI" controller type that is introduced after SCSI-2, in this large class also can launch two small classes according to the difference of the data bit width. If the original 8-bit parallel data transfer is referred to as "Ultra SCSI", its data transmission rate is 20mb/s, the maximum number of support connected devices to 8 units. In the parallel transmission of the bus bandwidth to 16-bit after the "Ultra Wide SCSI", its transmission rate has multiplied, that is, reached the 40mb/s, the largest number of supporting devices to connect 15 units.

(4) Ultra2 SCSI: It is the SCSI interface type that is introduced on Ultra SCSI basis. In 1997, the use of LVD (low voltage differential, low-level differential) transmission mode, allowing the maximum length of the interface cable 12 meters, which greatly increased the flexibility of the device; Like the SCSI connectors above, it is also divided into 8-bit narrow mode and adopt 16-bit wide mode. The 8-bit narrow mode is "Ultra2 SCSI", its transmission rate is 40mb/s, the maximum number of connected devices is 7, and the 16-bit Wide mode is called "Ultra2 Wide SCSI", which increases the transmission rate to 80mb/s, The maximum number of connected devices is 15 units.

(5) Ultra3 SCSI: It is the ULTRA2 SCSI update interface, which was introduced in September 1998 and includes new features in addition to supporting existing SCSI specifications and using the same interface cable and Terminator as Ultra2 SCSI. First, the ULTRA3 SCSI uses a dual-edge transmission frequency (double Transition clocking), and Ultra2 SCSI uses a single edge transmission frequency, so ULTRA3 SCSI transmission rate is twice times the former, that is, 160mb/s; SCSI also provides domain validation (domain Validation), CRC (cyclic redundant Check, redundancy loop correction), encapsulation (packetized Protocol), quick quorum selection (quick arbitrate & Select); To speed up the introduction of the ULTRA3 SCSI new technology, many vendors first introduced the ultra160/m scsi,ultra160/m SCSI technology and ULTRA3 SCSI, Just because there is no quick quorum selection and encapsulation, it can be said that ultra160/m SCSI is a subset of ULTRA3 SCSI.

(6) Ultra320 SCSI: It is all called "Ultra320 SCSI SPI-4" Technical specification. The Ultra320 SCSI single channel data transfer rate is up to 320m/s, and 640m/seconds can be achieved if a dual-channel SCSI controller is used. From the perspective of infrastructure development, 160m/s to 320m/s is technically not complex and expensive, so the transition from SCSI Ultra160 to Ultra320 SCSI is very easy for system integrators to implement.

The SCSI controller interface typically has 50 pins, 68 pins, and 80 pins, commonly used for 50 and 68 pins.

A SCSI card is a SCSI interface Add-in board that provides one or more (one interface over a cable to connect 15 SCSI devices) and can be plugged into a normal PCI (or pci-x) slot on a server (or other device) motherboard to provide multiple SCSI interfaces, To facilitate the connection of multiple SCSI peripherals.

The presence of a SCSI card solves two problems:

(1) A hard drive or other peripheral that is connected to a SCSI interface via a normal PCI slot (or a PC) that does not originally provide a SCSI interface to the motherboard;

(2) The number of SCSI interfaces has been extended because, in general, you can provide up to 2 SCSI interfaces in the server, and SCSI cards can provide up to 4 SCSI connectors. (as shown in Figure 1) is a Adaptec AHA39320 SCSI card that provides 1 68-pin, 2 external 68-pin SCSI connectors, a connection to the SCSI interface hard drive with a 68-pin SCSI interface, and an external SCSI interface for connection to a SCSI peripheral (including an external hard drive). This can connect up to 15 SCSI hard drives or 30 SCSI peripherals.