6500 Disk Array User’s Guide 21020690 B
Chapter 1 Description
Features and Options Page 1 - 5
the parity drive also significantly increases data availability—the length of time
before data is lost due to drive failure.
16-Bit Wide
Synchronous
Transfer
The controller has SCSI-P connectors (per the SCSI-2 standard) that permit 16-
bit wide synchronous data transfers over a single SCSI-P cable on the host
interface. The 6500 is a Wide Ultra SCSI device (SCSI-3), transferring data at
up to 40 MB/second.
Single-Ended
or Differential
Signals
Two methods can be used for sending signals on a SCSI bus—single-ended
and differential. Both are functionally equivalent and transparent to the
software protocol.
Note Single-ended and differential devices must not be combined on the
same SCSI bus. Each 6500 array must be initially ordered as either
single-ended (Model 6511) or differential (Model 6512).
• Single-Ended Option
The single-ended option permits the use of a single line for each signal.
The line's voltage varies between 0.5 and 3.0 volts DC, with a nominal
switching threshold at about 1.4 VDC. Maximum cumulative length of
single-ended cabling should not exceed 3.0 meters (approximately 10
feet).
• Differential Option
The differential option consists of two lines designated as a +SIGNAL
and a -SIGNAL. A signal is true when the +SIGNAL is more positive
than the -SIGNAL, and false when the -SIGNAL is more positive than
the +SIGNAL. The differential method is more immune to noise than
the single-ended method, and permits the use of much longer cabling—
up to 25 meters (approximately 82 feet).
Enclosure
Two horizontal mounting options are available—desktop and rack-mount. (For
information on rack-mounting the unit, see documentation included with the
optional rack-mount kit.)
