Network Servers: Everything You Wanted to Know but Were Afraid to Ask
were to simultaneously changed polarities, the parity system wouldn't detect the problem.
ECC memory is designed to address these problems. Systems using ECC memory can
detect up to two bits of errors and can automatically correct one bit of error. Most current
servers use ECC memory because of the added protection that it offers.
The third crucial performance subsystem for a server is its disk drives. Hard disk drives
are usually the slowest components of any system, and because most of the server's
work involves the hard disks, they are the components most likely to bottleneck the
system. Also, the data stored on a server is usually critically important to the company,
so it's important to have the most reliable disk configuration you can afford.
Disk Interfaces: SCSI Versus SATA
Two types of disk interfaces are in widespread use today: Serial Advanced Technology
Attachment (SATA) and Small Computer Systems Interface (SCSI). For a workstation
using Windows XP, SATA performs on par with a SCSI-based disk system. For a server
running Windows, Linux, or Novell NetWare, however, SCSI offers clear performance
advantages. SCSI systems perform much better when they have simultaneous access
to more than one hard disk and when they are used on an operating system--such as
the Windows server family or UNIX/Linux--that can take proper advantage of SCSI's
SCSI is pronounced "scuzzy." For a while, Macintosh users tried to adopt the pronunciation
"sexy," but it never took hold. (SCSI first saw widespread use on the Macintosh, at least in the
personal computing world.)
Many varieties of SCSI-based disk systems are available, as follows:
The basic SCSI specification can transfer data to and from the disks
at approximately 5 MBps using an 8-bit transfer width. Advances in SCSI
technology have made SCSI-1 obsolete, and it is not used on current systems.
(This is good because most SCSI-1 implementations weren't compatible with
This is the basic SCSI interface in use today. It extends the SCSI
specification and adds many features to SCSI, and it also allows for much faster
SCSI connections. In addition, SCSI-2 greatly improved the SCSI compatibility
between different SCSI device manufacturers.
With Fast SCSI, the basic SCSI-2 specification is enhanced to
increase the SCSI bus speed from 5 MHz to 10 MHz and the throughput from
5 MBps to 10 MBps. Fast SCSI is also called Fast Narrow SCSI.
Also based on SCSI-2, Wide SCSI increases the SCSI-2 data path
from 8 bits to either 16 or 32 bits. Using 16 bits, Wide SCSI can handle up to