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Step 8 Connect SCSI Cables
Cable Suggestions System throughput problems can occur if SCSI cable use is not maximized. You should:
•
you can use cables up to 12 meters for LVD devices
•
for single ended SCSI devices, use the shortest SCSI cables (no more than 3 meters for Fast
SCSI, no more than 1.5 meters for an 8-drive Ultra SCSI system and no more than 3 meters
for a 6-drive Ultra SCSI system)
•
use active termination
•
avoid clustering the cable nodes
•
cable stub length should be no more than 0.1 meter (4 inches)
•
route SCSI cables carefully
•
use high impedance cables
•
do not mix cable types (choose either flat or rounded and shielded or non-shielded)
•
ribbon cables have fairly good cross-talk rejection characteristics
Step 9 Set Target IDs
Set target identifiers (TIDs) on the SCSI devices. Each device in a specific SCSI channel
must have a unique TID in that channel. Non-disk devices (CD-ROM or tapes) should
have unique SCSI IDs regardless of the channel where they are connected. See the
documentation for each SCSI device to set the TIDs. The MegaRAID Express 500
controller automatically occupies TID 7 in the SCSI channel. Eight-bit SCSI devices can
only use the TIDs from 0 to 6. 16-bit devices can use the TIDs from 0 to 15. The
arbitration priority for a SCSI device depends on its TID.
Priority
TID
Non-disk devices (CD-ROM or tapes) should have unique SCSI
ID 0 cannot be used for non-disk devices because they are limited
to IDs 1 through 6. There is a limit of six IDs for non-disk devices
62
MegaRAID Express 500 Hardware Guide
, Continued
Highest
7
6
5
...
2
Important
IDs regardless of the channel they are connected to.
per controller.
1
0
15
14
...
9
Lowest
8
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