[SSI-devel] Re: shared SCSI-Device

[Andreas <ro...@co...>]

John Hughes wrote:
> Andreas wrote:

Hello

> 
>> Hello.
>>
>> I didn't work a lot with SCSI up to the moment and I wonder, which 
>> hardware is needed to use it with a single shared scsi-bus. At the 
>> moment I atach an single scsi-drive (with two HD50 connectors) with to 
>> scsi cables to two hosts. I suppose there is a problem with the 
>> termination? I read the documentation of kimberlite about this 
>> (http://www.missioncriticallinux.com/products/kimberlite_white_paper.pdf)
>> and there it say that an active pass-through terminator is needed. Is 
>> this correct? What is the difference between an active and a passive 
>> terminator and why couldn't the terminator of the host-adapter be used?
> 
> 
> The problem with using the host adaptor termination is what happens if 
> you turn one of the machines off.  Does the termination stay on?  With
> some Adaptec controllers it seems that the termination disappears when 
> the machine is turned off.

Well that could be, because one of the controllers is Adaptec. Is it 
possible to use an terminator on the internal SCSI Bus of each node? 
Would that have any effect if the power is off? Are there any cable for 
an external SCSI bus with more than 2 connectors? If there where it 
would be ease to use a simple terminator and not on with path-through.

> 
> Personaly I've had most luck with external disk cabinets that are smart 
> enough to provide their own termination if one of the two machines is 
> turned off, or even if the cable is disconnected (Dell 210, 211 and 221 
> with SEMM (SCSI Expansion Management Module).
> 
> I've also had problems with some old disks, e.g. Quantum Atlas IV, where 
> the disk seemed to hang if two machines tried talking to it.  You say 
> your disk has HD50 connectors, so I suppose it's pretty old.


The drive does not have that connectors. It is relative new. It is in an 
external case which has two outputs each with 50 Pins.
> 
> Did you remember to change the SCSI ID of one of the HBA's?#

Yes I did. The first is on 7 the second on 6. The drive is set to ID 1.


All I want to know is what the cost effective solution could be. It is 
only for test and not for productive use. I allready though about using 
the internal bus (flat cable) to connect first an terminator, then one 
host, then the drive, the second node and then an terminator. Would that 
alltough work?


Andreas

> 
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