UNIX System Administration Handbook - Evi Nemeth [82]
If you have more than one device on an IDE bus, you must designate one as the master and the other as the slave. Some older IDE drives do not like to be slaves, so if you are having trouble getting one configuration to work, try reversing their roles and make the other device the slave. If things are still not working out, you might be better off making each device a master of its own IDE bus.
When considering IDE hardware, keep in mind the following points:
• New IDE drives work on older cards, and old IDE drives work on newer cards. Naturally, only the features common to both devices are supported.
• The cable length is exceedingly short, which can make adding an extra device to the bus a stretch. If you experience random flakiness, check the cable length. A custom cable can make all the difference.
• Dealing with an old BIOS that does not see past the first 500MB of a disk is a bona fide nightmare. Check to see if the manufacturer has issued a firmware update to fix the problem. If not, you can replace the system’s motherboard for $100 or less; it’s worth it. Fortunately, BIOSes that old are rarely seen today.
• Well-designed drivers can significantly increase performance and reliability, especially when they support the most recent standards. Find out which features your driver supports (e.g., DMA and PIO modes) and compare those features to the range of options available in the marketplace. This is also good advice when you are shopping for disks.
Which is better, SCSI or IDE?
This is a frequently asked question that’s often waved away with talk about how each standard has its own advantages. However, we’ll go out on a limb and give you a straight answer: SCSI is better. Usually.
A more accurate answer would be that SCSI beats IDE in every possible technical sense, but SCSI equipment may not be worth the enormous price premium it now commands. For a single-user workstation, a good IDE disk is a simple, high-capacity, dirt-cheap solution that provides 85% of the performance of a SCSI setup. In most cases, upgrading a single-user workstation to SCSI will not increase the system’s perceived performance.
However, in some situations SCSI is advisable or even mandatory:
• If you absolutely must have the best possible performance, go SCSI. Part of the increased performance will come from SCSI’s technical superiority, but an even larger part will come from the fact that disk drive manufacturers use the IDE/SCSI divide to help them stratify the disk drive market. For business reasons, they simply don’t put IDE interfaces on the latest and greatest disk mechanisms.
• Servers and multiuser systems require SCSI. The SCSI protocol is unparalleled in its ability to manage multiple simultaneous requests in an efficient manner. On a busy system, you’ll see a concrete and measurable improvement in performance.
• If you want to connect many devices, SCSI wins again. SCSI devices play well with others; IDE devices hog and fight over the bus.
• You might need some particular feature that only SCSI provides. For example, it’s impossible to build a hot-pluggable disk array out of IDE drives.
8.2 DISK GEOMETRY
The geometry of a hard disk and the terminology used to refer to its various parts are shown in Exhibit B. This information is provided mainly to improve your general knowledge. Modern disk drives are still based on this same basic design,