ATTO Technology UL25 - Manual (Page 20)

Page 16 ATTO Technology, Inc.
A
PPENDIX
C: SCSI D
EVICE
& C
ABLING
L
IMITATIONS
Due to the electrical noise incurred with high-speed data transfer rates, SCSI has
cabling and device limitations. Table C-1 explains the maximum number of devices you
may use relative to your cable distance. For example, take the single-ended distance in
an UltraSCSI environment (Cells 3 & 4 in the single-ended bus length column). Look at
the corresponding cells in the maximum devices column to determine the maximum
number of devices you may connect at the specific distance. In an UltraSCSI
environment, using a single-ended bus length of 3 meters, you can only connect 4
devices. Using a single-ended bus length of 1.5 meters, you can connect up to 8 devices.
SCSI Type Single-Ended
Bus Length
Differential LVD Maximum
Devices
Fast SCSI 3 Meters 25 Meters 12 Meters 8
Fast/WIDE SCSI 3 Meters 25 Meters 12 Meters 16
UltraSCSI 1.5 Meters 25 Meters 12 Meters 8
UltraSCSI 3 Meters N/A N/A 4
Ultra/WIDE SCSI N/A 25 Meters 12 Meters 16
Ultra/WIDE SCSI 1.5 Meters N/A N/A 8
Ultra/WIDE SCSI 3 Meters N/A N/A 4
Ultra2 SCSI N/A N/A 12 Meters 8
Ultra2/WIDE
SCSI N/A N/A 12 Meters 16
Table C-1: UltraSCSI Cabling and Device Limitations
Table C-1 lists the maximum number of devices you may connect at specific cable
distances using differential and single-ended SCSI in various SCSI environments.
In an UltraSCSI workgroup environment with a 7-drive tower, you are limited to 1.5
meters between the host and tower (this distance includes the cabling in the tower). For
example, if the 7-drive tower requires 1 meter of cabling to connect all of its drives, the
distance from the tower to the host would be .5 meters. Adding an ATTO SCSI Sidekick
to this configuration would increase the distance between the host and tower to 2
meters.
Ultra2 SCSI is less sensitive to SCSI bus noise and offers you the ability to connect a
full load of devices up to 12 meters. Use table C-1 to assist you when attempting to
configure your workgroup. If you have any questions or issues occur with your
configuration, please call an ATTO technical support representative.