Hard drives can be a big performance bottleneck. While IDE drives are cheaper than bricks, they can slow down your system roughly as well as bricks can. A SCSI disk system can transfer data to and from each and every drive on the SCSI bus at the full speed of the SCSI controller, while an IDE controller splits its available throughput between the drives on the bus. Also, a SCSI controller can have up to 15 drives, while an IDE controller can have no more than 2. In a throughput competition, I'll back 15 drives moving at full speed against 2 drives moving at an average of half-speed any day.
Still, if all you have are IDE drives, you can do some things to alleviate these problems. Most important, put your hard disks on separate controllers! Many systems now have a hard drive on one IDE controller and a CD-ROM on the other. When you add a second hard drive, put it on the same controller as the CD-ROM drive. You probably won't be using the CD-ROM nearly as often as you use the hard drive, after all, and this will reduce contention on each IDE channel.
SCSI 果然比 IDE 快了很多。而在有多个硬盘的情况下，把它们分别置于 IDE-0、IDE-1 比较好，可以减少“contention on each IDE channel”，毕竟我们使用 CD-ROM 的时间远低于我们使用硬盘。
:-) ... 以后加新硬盘的时候就注意一下，呵呵~