Device mixing

The best way to mix different SCSI types, such as wide and narrow, is to use a host adapter that supports segmentation. In this configuration, each segment has its own cabling and termination that won’t conflict with the other. Using different SCSI types on the same bus channel is possible, but you should keep in mind some important configuration items. You will need to use cable adapters that will facilitate connections between 50-pin devices and 68-pin wide devices. Ensure that these special cables support termination so a wide-to-narrow adapter will terminate the extra wide connections.

Linux SCSI devices

You can find the device names of SCSI devices within the /dev directory. For SCSI disk drives, the /dev directory contains IDs for each of the drives. For example, the first drive on the first SCSI bus is called /dev/sda, and the second drive is /dev/sdb. Each disk is divided into partitions, such as /dev/sda1, or /dev/sdb2.

SCSI CD-ROM devices have traditionally used /dev/sr as an identifier, but more recent distributions use /dev/scd, so the first CD-ROM is /dev/scd0.

SCSI tape devices are slightly different — as the device name indicates — if the tape will or won’t use rewind. For example, the first tape drive is /dev/st0, but the first tape with no rewind uses /dev/nst0.

Most other SCSI devices, such as scanners, use the device names of /dev/sg0, /dev/sg1, and so on.

ATA/IDE Devices

7.2 Assure that system hardware is configured correctly prior to installation (e.g., IRQs, BIOS, DMA, SCSI settings, cabling) by identifying proper procedures for installing and configuring ATA devices

7.6Remove and replace hardware and accessories (e.g., cables and components) based on symptoms of a problem by identifying basic procedures for adding and removing field replaceable components

7.7Remove and replace hardware and accessories (e.g., cables and components) based on symptoms of a problem by identifying common symptoms and problems associated with each component and how to troubleshoot and isolate problems

7.9 Identify proper procedures for diagnosing and troubleshooting ATA devices

ATA/IDE is the most often-used disk type on desktop systems. IDE (Integrated Drive Electronics) places the bulk of the IO “intelligence” on the disk controller card. Early drives had a separate controller and disk drive.

Most new ATA drives are available in the following types:

Ultra ATA/33: Includes UDMA (which is an advanced DMA technique that essentially doubles the speed of data transfer clocking) allowing a throughput of 33 MB/s. ATA/33 also introduced a new 80-conductor IDE cable to support reliability with the faster speeds. It also uses CRC (Cyclical Redundancy Checking) to provide error checking.

Ultra ATA/66: This type of drive features faster UDMA modes that allow up to 66 MB/s data transfer. The special 80-conductor IDE cable, which was optional with ATA-33, is mandatory for ATA-66.

Ultra ATA/100: The latest standard that brings data transfer speeds to

100 MB/s, and also improves LBA support for extremely large hard drives.

IDE drive configuration

One IDE channel can support up to two devices. To differentiate between the devices, one drive is configured as the master drive and the other as the slave. No performance difference exists because these are just identifiers for the drives. It is often easier to think of master and slave alternately as Drive 0 and Drive 1.

You must follow certain rules when configuring the master and slave designations for IDE hard drives. With two devices present, one must be configured to be the master, and the other the slave. You can’t have two masters or two slaves; this will typically result in a boot failure because the system won’t be able to properly identify the boot disk drive.

Some systems also have a third option, called cable select, in which the master and slave are configured using a special cable with specific connectors for each drive.

Jumpers

IDE drives use jumpers to set their configuration. A jumper is a small connector that fits over two pins on the hard drive. The jumper will make a connection between those two pins to signal the configuration for the hard drive. Even though manufacturers have their own sets of pins on the hard drive for these configurations (typically six to ten pins), most pin configurations are generally the same.

Typically, the proper settings for the jumpers are printed on the hard drive, but you may have to consult the manufacturer’s documentation or Web site for the information.

Master/Slave settings

To set the drive as the Master: Use a jumper to join the two pins that are labeled as Master or “MA.” Most hard drives ship from the manufacturer configured as the master, so you may have to adjust the jumper if you need to use the hard drive as a slave.