[CentOS] Mixing SCSI devices on a single i/f

Joshua Baker-LePain jlb17 at duke.edu
Wed Sep 21 15:07:19 UTC 2005

On Wed, 21 Sep 2005 at 10:49am, James B. Byrne wrote

> I have an external HP SureStore DLT VS80 with a SCSI LVD 68 pin 
> interface and an external HP SureStore DAT24 with a SCSI Centronics 
> 50 pin Narrow SE interface.  The cable for the DAT has a Centronics 
> connector at one end and a 68 Pin Wide to Narrow terminated 
> connector at the other. The cable for the DLT has a LVD/SE 68 pin 
> connector at both ends.  I have terminator blocks for both devices.


> My question is: Is it possible to daisy-chain these two devices to 
> the host in manner that permits the system to boot and access both; 
> and if so, how does one accomplish this?

It should be possible, but it's generally not recommended.  Having even 
one SE device on a LVD chain drags every device on the chain down to SE.  
In addition to reducing the SCSI bus speed, you're also severely limiting 
your cable length.

To accomplish the mixing, you have to make sure that the wide->narrow 
converter is *active*, not passive.  I don't know that I've ever seen a 
cable with an active wide->narrow converter.  You'll likely have to buy an 
adapter.  And, again, if you go this route, check the standard and make 
sure you're not over the allowed SE cable length.  It's awfully short.

Given that you're likely to have to buy an adapter, why not just buy a 
cheap SE SCSI card instead and have each drive on its own bus?

Joshua Baker-LePain
Department of Biomedical Engineering
Duke University

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