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In Article <824050290.7987@eurofinn.demon.co.uk>
thomas@highland.scotnet.co.uk (Thomas Woodrow) Wrote: 

> Does anyone out there agree with a policy of seperate SCSI cards for 
> each device? Could the clash have damaged any part of the machine 
> (thought to be very unlikely).

A lot depends on the requirements of your system or SCSI Subsystems
in general, personally I have had 3 SCSI HD's, 1 DAT drive, CDROM 
and a Scanner hanging off one card, no problems, sionce I started working 
in serious server enviroments I can see the reasoning behind it in _SOME_
cases, DAT's move data at around 512K per second on good ones,
CD's can do similar under burst rates, why tie up a bus with slow devices
when you can stick them on a single card....leave the fast stuff for HD's..

Scanning is slightly differant, it is unlikely that you will use much else 
when scanning because of the CPU usage of the scanning software.
However I suppose it is possible for the Polling to a CDROM drive
to interupt the flow of scanned data to the HD...

Having said that the CDR's are differant, when you write to one (or so
I have been told) you need to write your data in one continuous stream of
data stop for a second and you may be looking at a corrupted disk.

It is important to leave the machine alone with making your discs
and probably a good idea to have a seperate card with its own buffering
on it to fill any gaps you might get, some cards like the Adaptec seem to 
continually poll devices such as CDROMs, the light seems to flicker
every coupla seconds, I have seen this a few times with various systems,

My Dec Server 590 is no differant..

A recent server I installed had 4 SCSI cards installed, 2 embedded 
SCSI-2 FAST Adaptec controllers and 2 DPT controllers, no corruption
and no problems..

If you actually had both cards working it is unlikely that the crash or
data corruption was caused by them but SCSi cards can be funny
(or Not) beasts..

The hardest thing is to actually get them all working in the first place..
Since you had that I cant really offer an explaination for the corruption.

If you need any more info feel free to E-Mail me..

--------------------------------
- Steve Robertson, stever@mistral.co.uk, Worthing, UK
- 
- The opinions expressed are my own.
- (disclaimer)
- The above is still true, unless I decide to make up a
- fictional expert or guru, then the opinions belong to them.
 

Thomas, 

This does not sound like a normal HP recommendation.  As a whole, HP
knows SCSI well enough not to tell people one SCSI adapter per device.
That defeats the purpose of SCSI, to support up to 8 (even more with
SCSI-3) devices per host adapter.

What you DO need however is a full-featured SCSI host adapter, rather
than the crippled ones delivered on a one off basis with single SCSI
peripheral devices. 

I've had decent experience with both Adaptec and BusLogic SCSI host
adapters and suggest you get one of these (depending on the bus in
your computer, you would need to buy a different model.  Make sure
that you get an adapter packaged with a SCSI host manager, and you
should be all set to connect up to 7 various and sundry devices up to
your computer.  Other people can give you specific recommendations re.
SCSI host adapters from other vendors.

Best regards,
Ben Myers

thomas@highland.scotnet.co.uk (Thomas Woodrow) wrote:

>A SCSI clash:
>Why do Hewlett Packard recommend one SCSI adapter card per device???
>Here's a problem concerning HP's Scanjet scanner and Surestore 
>writeable CD ROM. I'm sure that the advice being given out by
>manufacturers may well be 
>wrong in some circumstances:

>A friend's scanner came with its own 8 bit card which, while there was

>only a scanner as a SCSI device in the computer, worked very well.
>Next, a 
>Surestore was fitted and it came with its own 16 bit SCSI card. Since 
>SCSI interfaces should support up to 7 devices or more, we checked
>with Hewlett  Packard about whether to continue using the existing
>SCSI card for the scanner  and additionally install the new one for
>the Surestore. They advised that we should (as does the Surestore
>manual). This seemed wrong to us but the manual and HP indicated it
>was  the right way to go...

>Problems started straight away: intermittent hard disk lock up,
>Windows 3.11 file 
>manager deleting files instead of renaming (as selected), crashes and 
>system lock up. A large number of  expensive international calls to HP
>later, and they agreed with our thinking after all - the scanner and
>the Suretore should be fitted to one common SCSI card. But they had no
>idea if they had such a product or how it could be accomplished!

>The motherboard is a PCI board fitted with a CYRIX 586 100MHz chip, 
>256K cache, 32Mb RAM, internal mode 4 EIDE Hard disk controller and
>its fitted with a Seagate 1Gb mode 4 drive and a Conner 850Mb mode 4.

>Why are HP advising fitting a seperate SCSI interface for each 
>peripheral. Does this not defeat the whole logic behind SCSI? What if 
>this person gets a third SCSI device and then a fourth? Where will
>they  fit the interface cards? Why don't HP supply a 16 bit or PCI
>SCSI adapter board with a internal terminated connector for the
>Surestore and an external socket for other devices like the Scanner
>(or indeed an external kit to daisy chain the Surestore with other
>devices?)

>Does anyone out there agree with a policy of seperate SCSI cards for 
>each device? Could the clash have damaged any part of the machine 
>(thought to be very unlikely).
>Thanks for any views.
>Thomas.