Dell PERC 4/DC - Manual (Page 58)

4. The host controller has a SCSI ID of 7.
5. Connect the cable to the devices.
Cable Suggestions
System throughput problems can occur if the SCSI cables are not the correct type. To avoid problems, you should follow the following cable suggestions:
l Use cables no longer than 12 meters for Ultra3, Ultra160, and Ultra320 devices. (It's better to use shorter cables if possible.)
l Make sure the cables meet the specifications.
l Use active termination.
l Note that cable stub length should be no more than 0.1 meter (4 inches).
l Route SCSI cables carefully and do not bend cables.
l Use high impedance cables.
l Do not mix cable types (choose either flat or rounded and shielded or non-shielded).
l Note that ribbon cables have fairly good cross-talk rejection characteristics, meaning the signals on the different wires are less likely to interfere with
each other.
Step 6 Set Target IDs
Set target identifiers (TIDs) on the SCSI devices. Each device in a channel must have a unique TID. Non-disk devices 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 RAID controller automatically occupies TID 7, which is
the highest priority. The arbitration priority for a SCSI device depends on its TID.
Table 3 -3 lists the target IDs.
Table 3-3. Target IDs
Step 7 Set SCSI Termination
The SCSI bus is an electrical transmission line and must be terminated properly to minimize reflections and losses. Termination should be set at each end of
the SCSI cable(s).
For a disk array, set SCSI bus termination so that removing or adding a SCSI device does not disturb termination. An easy way to do this is to connect the
RAID controller to one end of the SCSI cable and an external terminator module at the other end of the cable, as shown in
Figure 3 -4 .
The connectors between the two ends can connect SCSI drives which have their termination disabled, as shown in the drives (ID0, ID1, ID2) attached in the
figure. See the manual for each SCSI drive to disable termination.
Set the termination so that SCSI termination and TermPWR are intact when any hard drive is removed from a SCSI channel.
Figure 3-4. Terminating Internal SCSI Disk Array
NOTE: The maximum cable length for Fast SCSI (10 MB/sec) devices is 3 meters and for Ultra SCSI devices is 1.5 meters. The cable length can be up to
12 meters for LVD devices. Use shorter cables if possible.
Priority Highest Lowest
TID 7 6 5 ... 2 1 0 15 14 ... 9 8