SCSI接口的些许知识以及其在linux中应用

SCSI的英文名称是“Small Computer System Interface”,中文翻译为"小型计算机系统专用接口";顾名思义,这是为了小型计算机设计的扩充接口,它可以让计算机加装其他外设设备以提高系统性能或增加新的功能,例如硬盘、光驱、扫描仪等。
早期的计算机依速度、功能被区分为大型主机、小型计算机、微型计算机等多种等级,部分小型工作站、服务器属于小型计算机,而个人计算机属于微型计算机;因此当时使用SCSI接口的机种也以工作站、服务器等中高档设备为主。近年来则因个人计算机性能、扩充需求均大增,使SCSI在PC（普通微机）的应用也越来越多。

其实,SCSI也不算是新的接口类型,从有人注意到小型计算机功能延伸的问题、开始发展新的统一扩充接口、并在1986年正式订下SCSI的标准,至今也经历了将近20年的时间。早期Apple（苹果电脑）公司率先将SCSI选定为Macs计算机的标准接口,许多外设都借此统一接口与主系统连接。在PC方面则因为SCSI接口卡和设备昂贵,并且几乎各种外设都有较便宜的接口可替代,SCSI并未受到青睐;相对的,可用的SCSI设备也就不多了。反观今天,支持SCSI接口的外设产品从原本仅有硬盘、磁带机两种,增加到扫描仪、光驱、刻录机、MO等各种设备,大家接触SCSI的机会正在逐步增加中;再加上制造技术的进步,SCSI卡与外设的价格都已经不再高高在上,显示SCSI市场已经相当成熟。

以上信息来源：http://publish.it168.com/cword/1456.shtml

SCSI devices under Linux are often named to suite the device. For example the first SCSI tape drive is /dev/st0. The first SCSI CD-ROM is /dev/scd0. These devices do not have partitions and do not use letter identifiers. SCSI disks are labled /dev/sda, /dev/sdb, /dev/sdc etc... to represent the first, second, third,... SCSI hard drives but they do not reflect the SCSI ID. SCSI hard drive partitions are represented by an additional number. i.e. First drive first partition, /dev/sda1, second partition, /dev/sda2,... The drive names are incremented across multiple SCSI HBA's (cards) as if it is all one device. When using scanners, one uses the "raw" device name.

SCSI ID Number	Linux Device (raw name)
0	/dev/sga
1	/dev/sgb
2	/dev/sgc
3	/dev/sgd
4	/dev/sge
5	/dev/sgf
6	/dev/sgg
7	/dev/sgh

The SCSI device number 7 is usually reserved for the SCSI card itself.
To list scsi devices on Linux system: cat /proc/scsi/scsi

SCSI will use a controller ID, channel ID, unit ID and LUN (Logical unit number).

List partition table: fdisk -l

Linux SCSI Notes:

One can verify that the SCSI driver module has been loaded with the command: /sbin/lsmod
```
..
...
aic7xxx               130932   5
...
..
```
Typical listing for the Adaptec driver aic7xxx.
The SCSI driver module can be loaded manualy with the command: insmod aic7xxx
The modules to be loaded upon system boot are listed in the file: /etc/modules.conf
Options (seek order and debug options) for the Adaptec SCSI module can be listed in the file: /etc/modules.conf
The latest Adaptec drivers can be found at http://people.freebsd.org/~gibbs/linux/ in driver install floppy "img" format, Red Hat RPMs and as source code.
See this pitfall if you have data corruption problems
Installing Red Hat Linux on a system for which a new adapter driver does NOT exist, you must provide it during installation. Download the "img" floppy image from http://people.freebsd.org/~gibbs/linux/ and write it to a floppy: dd if=aic7xxx-6.2.36-i686.img of=/dev/fd0 bs=1440k You will be prompted for the floppy during installation.

SCSI Hardware:

SCSI Interfaces and standards:

SCSI Type	Description	Transfer speed per channel	Number of pins
SCSI-1	Mid 1980's era	5 MB/sec	50 pin Centronicx (CN50)
Fast SCSI	Fast SCSI-2, 8 bit. Currently used primarily for peripherals. i.e. scanners, CD ROM, zip drives, ... (Adaptec 2906)	10 MB/sec	50 pins (DB50)
U	Ultra SCSI, 8 bit (Adaptec AHA-2930, AHA-2940)	up to 20 MB/sec	50 pins (DB50)
UW	Ultra Wide SCSI, 16 bit (Adaptec AHA-2940UW, AHA-2944)	up to 40 MB/sec	68 pin Ultra Wide SCSI-2 [50 pin SCSI peripherals]
Fast UW	Ultra2 Fast and Wide SCSI, 16 bit	up to 80 MB/sec	68 pin Ultra Wide SCSI (Micro D68) [50 pin ultra SCSI peripherals]
U160	Ultra3 160, 16 bit, LVD (Adaptec 29160)	up to 160 MB/sec	68 pin, LVD cable (Micro D68) [50 pin ultra SCSI peripherals]
U320	Ultra3 320, 16 bit, LVD (Adaptec 29320A-R)	up to 320 MB/sec	68 pin, LVD cable (Micro D68) 68 pin wide ultra [50 pin ultra SCSI peripherals]

Terms:

LVD: Low Voltage Differential SCSI
HVD: High Voltage Differential SCSI

以上来源：http://www.yolinux.com/TUTORIALS/LinuxTutorialSCSI.html

我们在linux系统下操作，若能识别则是很简单的事情，但是遇到故障或系统不能识别，那么问题就奇怪有之、无法解释有之，唯其原理可靠也！