problems with fast wide SCSI ext. HD

[wayne johnson_1]

We have a HP UNIX c110/9000 running OS10.20.B.

We just tried to connect an external HD ( Fantom Drive 36 GB) with an Ultra2 SCSI interface. to the back of our HP machine via the Fast, Wide SCSI port.

Also, I set the SCSI ID on the ext. HD to 9 as not to conflict with any other devices listed in from the ioscan command.

My problem is that after attempt to boot up the HP machine it cannot find a bootable device. I even select the root disk manually via the console mode but it still fails.

The machine will boot just fine if the ext. HD is removed. Also, the ext. HD vendor said that an Ultra2 should work for a fast, wide SCSI port.

Please help .

Thanks,
Wayne

[Bill Hassell · Accepted solution]

Unfortunately, the vendor is unaware of the two, completely incompatible SCSI standards. FWD, when used in conjunction with older HP computer products means: FastWideDifferential - HighVoltage, while the vendor is selling you a FWD - LowVoltage disk--which will cause the symptoms you are seeing.

FWD-HV was popular many years ago because of the very long cables that could be used. And to make things worse, the connectors are identical to the much newer FWD-LV disks that are available today. Be sure you get FWD-HV disks for this computer's FWD port.

[A. Clay Stephenson]

Hi Wayne:

My first thought is that you are mixing FWD SCSI with LVD/SE which is also known as Ultra2 SCSI. It depends on the exact interface your C-box is using. If you mix the type bus types it is possible to take out the drive(s) and/or controller. Be very careful and check the specs. P.S. Smoke is generally considered to be a bad thing.

Regards, Clay

[Helen French]

Hi,

The C110 Workstation comes with a Fast wide differential SCSI interface. You won't be able to connect a Ultra2 SCSI (LVD/SE) disk to this.

Do you have the Product numbers for the Disk and the controller ? If you are trying to mix the bus, then you will experience lot's of problems.

HTH,
Shiju

[Gregory Fruth]

There's a appalling number of different SCSI types,
and you've found one of the many combinations
that doesn't work.

The table at the link below may be of interest:

http://www.scsita.org/terms/scsiterms.html

The compatibility rules I go by are:

Wide must go with Wide
Narrow must go with Narrow
LVD can go with LVD or SE
HVD must go with HVD
Ultra3 can go with Ultra3, Ultra2 or Ultra
Ultra2 can go with Ultra2 or Ultra
Ultra can go with Ultra
Fast must go with Fast
Slow must go with Slow

I don't know how Ultra(1,2,3) match up with Fast or Slow,
or if Fast and Slow work together.

With any allowable mismatched combination, you always
get the worst performing one: e.g. when connecting an
Ultra2 drive to an Ultra bus, the drive switches down to
Ultra.

Some combinations that violate the above may work,
but may require special adaptors. I would avoid them
if at all possible.

[Gregory Fruth]

P.S. Since FWD drives may be difficult to find these days,
you may want to look at HP's A4974A PCI SCSI adaptor:

http://www.hp.com/workstations/products/accessories/unix/io_cards/a4974a/summary.html

It will support more modern (vs. FWD) drives like Ultra Wide
Single Ended (UWSE) and Ultra2 Wide LVD (U2W-LVD).
However, U2W-LVD drives will switch down to the UWSE
speed and signalling, so you lose some performance and
will have a pretty limited maximum cable length. Also, for
the C110, the boot device cannot be on the A4974A.

The A4999A would be even better since it supports
U2W-LVD directly, but I don't think it will work in a
C110.

http://www.hp.com/workstations/products/accessories/unix/io_cards/index.html