I'm curious as to how you got 16 drives on one FW.   The limit is 15 SCSI
addresses.  If you are using an array, you can have multiple LUNS on each
SCSI address.  I don't know if there is a configuration maximum but the FW
interface has limited IO throughput.  For performance reasons, I've limited
the DISC per FW channel to no more than 80Gb.   The configuration is based
on the throughput required by the application, not the physical limitation
although I'm sure there is one.   The most we have configured on any channel
is 140Gb using 20 x 7Gb LUNs on an XP256 array.  This uses 5 LUNS on 4 SCSI
addresses on the same channel.


Eucaristo,
Tom Genute
Phone:  (212) 437-1744
Pager:   (888) 778-7121


                -----Original Message-----
                From:   Steve Dirickson [mailto:[log in to unmask]]
                Sent:   Friday, February 18, 2000 9:13 PM
                To:     [log in to unmask]
                Subject:        Re: Number of Disk Drives

                > 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
                [log in to unmask]   (360) 598-6111