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ATTO Technology Inc. FastStream Installation and Operation Manual
Appendix A Cabling
Additional information to physically connect ports to devices and to your SAN.
SCSI cabling
Cables and devices must be chosen to maximize
performance and minimize the electrical noise
from the high-speed data transfers available with
the SCSI protocol. Cabling and termination
methods become important considerations for
proper performance. SCSI cables and devices are
subject to specific length and number limitations
to deal with electrical problems that arise at
increased operating speeds.
Cable types
Use high-quality cables rated for the type of SCSI
transfers required: well-insulated SCSI cables
ensure error free communications. Try to keep
cable lengths as short as possible to ensure higher
signal quality and performance.
Examples
The SCSI specification limits total bus cable
length for single-ended SCSI in a non-UltraSCSI
environment to 3 meters (combined length of both
internal and external cable lengths).
In an UltraSCSI workgroup environment with a 7-
drive tower, you are limited to 1.5 meters between
the host and the tower, including the cabling for
the tower. If the 7-drive tower requires 1 meter of
cabling to connect all of its drives, the distance
from the tower to the host must be .5 meters.
Note
UltraSCSI is very sensitive to SCSI bus noise,
cable distances and the number of devices
connected on the SCSI bus. Carefully connect
your devices when working with UltraSCSI.
Appendix exhibit 1 Various types of SCSI operate at different speeds and require different bus lengths to
support a certain number of devices.
Connecting SCSI devices to SCSI ports
ATTO FastStream NDMP 4600 SCSI ports
connect SCSI storage devices to the network.
Each SCSI port is completely independent from
the other SCSI port.
Each SCSI port is a bus capable of supporting 15
devices and each bus is capable of 40, 80, 160 or
320 MB/sec. (Ultra, Ultra2, Ultra 160 or Ultra
320) transfer rates.
You may use externally provided striping
software to create a RAID 0 group that includes
devices from both SCSI busses to increase overall
performance.
Each SCSI bus auto-negotiates the appropriate
sync rates with the connected devices. If slower
STA terms
Bus speed
MB/sec. max.
Bus width
bits
Max. bus lengths in meters
Max. device
support
Single-ended
Differential
LVD
Fast SCSI
10
8
3
25
n/a
8
Fast/WIDE SCSI
20
16
3
25
n/a
16
UltraSCSI
20
8
1.5
25
n/a
8
Ultra/WIDE SCSI
40
16
n/a
25
n/a
16
WIDE Ultra SCSI
40
16
1.5
n/a
n/a
8
WIDE Ultra SCSI
40
16
3
n/a
n/a
4
Ultra2 SCSI
40
8
n/a
n/a
12
8
WIDE Ultra2 SCSI
80
16
n/a
n/a
12
16
Ultra 160 SCSI
160
16
n/a
n/a
12
16
Ultra 320 SCSI
320
16
n/a
12
n/a
16
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