> We have a 987/200 running MPE/iX 5.5 pp 7 with a few reactive
> patches thrown
> on for good measure. I am trying to find out how many disks I
> can hang off
> of one FW/SCSI. I am interested in throwing all the rules
> about performance
> and stability and the dip switches on the hardware out the door. I am
> interested in just the path limitations. Currently 987 is not
> being used at
> night. I currently have the EMC BCV back up procedure in
> place on our test
> machine and would like to move it. We only have two slots
> available on the
> 987 and moving the back up would exceed the 15 limit by
> almost double. We
> also have a machine that currently has 16 drives on one
> FW/SCSI and it works
> fine so I know the limit of 15 can be exceeded, I just don't
> know by how
> much. If anyone has put more than 15 drives on one FW/SCSI I
> would like to
> know how many as this amount may be high enough to let me
> know I can do what
> I want. I also have HP looking into this for me.

A 16-bit SCSI channel (a.k.a. "Wide" SCSI) supports 16 targets, one of which
is the adapter. Each of the other 15 targets can be drives, scanners, other
adapters, whatever, but there are only 15 targets available. Each target may
contain up to 8 Logical Unit Numbers (LUNs). Relatively few devices use
LUNs; I've seen them used in CD and tape changers. If none of the target
devices on the bus use LUNs, the maximum number of devices on the bus (other
than the adapter) is 15. If all targets use LUNs, 120 devices can be
addressed. I've never seen a stand-alone disk drive that uses LUNs, though
they may exist.


Steve Dirickson   WestWin Consulting
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