[Info-vax] SCSI cable rules.

[Tom Adams]

On Thursday, September 1, 2016 at 11:31:03 AM UTC-4, Stephen Hoffman wrote:
> On 2016-09-01 13:56:37 +0000, Tom Adams said:
> 
> > We have DS10s and I am trying to avoid SCSI cable pitfalls.
> 
> Please read the old DEC SCSI developer docs for details on how DEC 
> envisioned the SCSI pieces would fit together.  Link here: 
> http://labs.hoffmanlabs.com/node/54
> 
> See other available resources, as well: 
> http://computer.howstuffworks.com/scsi4.htm   
> http://www.pcguide.com/ref/hdd/if/scsi/prot_Diff.htm  
> http://www.pcguide.com/ref/hdd/if/scsi/protLVD-c.html
> 
> Stay far, far, far, far, far away from HVD SCSI, until and unless 
> you're very sure you have compatible equipment:  
> http://www.pcguide.com/ref/hdd/if/scsi/z_t10_iconhvd.gif
> 
> Or use some of the old DEC- or Compaq-branded external SCSI shelves 
> http://labs.hoffmanlabs.com/node/54 and avoid most of the mess of 
> internal drives and cabling and canted connectors and skinned knuckles.
> 
> > I have some SCSI cables with no terminator on the end, it was probably 
> > a mistake to buy those.  Looks like most of the disks and tape drives 
> > we have don't have a "terminator" jumper.  Some have "term power" 
> > jumpers. The passive female terminators for internal 68 pin cables seem 
> > to be kind of pricy and bulky.
> > 
> > Can I assume that all the SCSI control cards that work for a DS10 will 
> > provide term power so that I don't have to add a device that has term 
> > power?
> 
> There's little or no reason to put a SCSI terminator in a cable.   Even 
> the internal ribbon cables have separate terminators plugged into the 
> connector, not integrated into the cable.  Or the terminator is plugged 
> into the last device in the chain.   A SCSI terminator is a SCSI 
> terminator, differing by details such as wide or narrow bus, active or 
> passive, and the specific connector used.
> 
> Simpler is better.   Use shelves.   Makes cabling simpler.   Makes 
> disks easier to swap.
> 
> 
> -- 
> Pure Personal Opinion | HoffmanLabs LLC

I think you are right about using shelves.  I will start planning in that direction.

Another advantage to shelves is a quicker restore if the computer fails.  I can just disconnect the disk box and connect it to another computer, quicker than opening the computer.  We have disk shadowing.