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On Apr 9, 2004, at 2:01 PM, Erik E. Fair wrote:

> NetBSD supports at least three busses that can have multiple hosts on 
> them: SCSI, FireWire, and USB.

USB does not support multiple hosts.  However, we also can talk to 
Fibre Channel.

>  Has anyone we know actually tried to share, say, a disk between 
> multiple hosts on the same SCSI bus? Obviously for that case, some of 
> the host SCSI IDs would have to be pre-set to something other than 7, 
> and after that, there is a question of access arbitration and cache 
> coherency...

This requires some complex coordination.  For starters, we would need 
to support the SCSI RESERVE/RELEASE (older) and newer persistent 
reservation commands.  Then other software (like the file system) has 
to be taught how to use them.  That can be Very Hard for fairly simple, 
depending on the sharing model you want to employ.

         -- Jason R. Thorpe <thorpej@wasabisystems.com>


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