Document

Integration Guide for New Dual-Core Intel
®
Xeon
®
Processor-Based Servers (or Workstations) Rev 1.1
16
It is recommended to use the hot swap and redundant power supplies for new Dual-Core Intel
®
Xeon
®
processor-based servers. Hot swapping a power supply is the process of inserting and extracting a
power supply from a server while it is operating, without interruption.
3.6 Other System Components
3.6.1 Hard drive
1) SCSI HDD
The SCSI specification was developed to provide a common interface that could be used across all
peripheral platforms and system applications. The SCSI interface addresses a wider range of
applications, such as Redundant Array of Independent Disks (RAID) storage, and has a broader
command set than the parallel ATA interface. The SCSI system contains the SCSI controller (initiator),
the SCSI bus (cable or backplane), and one or more target devices. The SCSI controller may be built into
the motherboard or housed on a SCSI host bus adapter (HBA) card in a PCI or PCI-X slot. Both
configurations are shown in Figure 3.6.1.
SCSI cables can connect up to 16 devices, including the SCSI controller. SCSI cables consist of 34 twisted
pairs of multi-stranded flexible copper wires for a total of 68 conductors. SCSI devices inside the server
are connected to the SCSI controller by a 68-pin ribbon cable. The ribbon cable has a connector at each
end and one or more connectors along its length. External SCSI devices are attached to the SCSI HBA by
a round 68-pin cable. Two sets of terminators, one at each end of the SCSI bus, prevent signal reflections
within the cables.
Figure 3.6.1 SCSI components
Since 1981, there have been seven generations of the SCSI protocol. Each new generation has doubled
the performance of the previous one (Figure 3.6.2). SCSI performance has ranged from an 8-bit,
single-ended interface transferring data up to 4 MB/s (SCSI-1) to the latest 16-bit, low-voltage
differential interface transferring data at 320 MB/s per channel (Ultra320 SCSI).