About IDE, SATA, and SCSI Drives

IDE Drives

To save costs, many small business systems will probably use IDE disks, but they do have some limitations.

• The total length of an IDE cable can be only a few feet long, which generally limits IDE drives to small home systems.
• IDE drives do not hot swap. You cannot replace them while your system is running.
• Only two devices can be attached per controller.
• The performance of the IDE bus can be degraded by the presence of a second device on the cable.
• The failure of one drive on an IDE bus often causes the malfunctioning of the second device. This can be fatal if you have two IDE drives of the same RAID set attached to the same cable.

For these reasons, I recommend you use only one IDE drive per controller when using RAID, especially in a corporate environment. In a home or SOHO setting, IDE-based software RAID may be adequate.

Serial ATA Drives

Serial ATA type drives are rapidly replacing IDE, or Ultra ATA, drives as the preferred entry level disk storage option because of a number of advantages:

• The drive data cable can be as long as 1 meter in length versus IDE's 18 inches.
• Serial ATA has better error checking than IDE.
• There is only one drive per cable which makes hot swapping, or the capability to replace components while the system is still running, possible without the fear of affecting other devices on the data cable.
• There are no jumpers to set on Serial ATA drives to make it a master or slave which makes them simpler to configure.
• IDE drives have a 133Mbytes/s data rate whereas the Serial ATA specification starts at 150 Mbytes/sec with a goal of reaching 600 Mbytes/s over the expected ten year life of the specification.

If you can't afford more expensive and faster SCSI drives, Serial ATA would be the preferred device for software and hardware RAID

SCSI Drives

SCSI hard disks have a number of features that make them more attractive for RAID use than either IDE or Serial ATA drives.

• SCSI controllers are more tolerant of disk failures. The failure of a single drive is less likely to disrupt the remaining drives on the bus.
• SCSI cables can be up to 25 meters long, making them suitable for data center applications.
• Much more than two devices may be connected to a SCSI cable bus. It can accommodate 7 (single-ended SCSI) or 15 (all other SCSI types) devices.
• Some models of SCSI devices support "hot swapping" which allows you to replace them while the system is running.
• SCSI currently supports data rates of up to 640 Mbytes/s making them highly desirable for installations where rapid data access is imperative.

SCSI drives tend to be more expensive than IDE drives, however, which may make them less attractive for home use.