Re: [Stgt-devel] Question for pass-through target design

[Vladislav Bolkhovitin <vst@vlnb.net>]

Robert Jennings wrote:
>>>>What I meant that is that the kernel tgt code (scsi_tgt*) receives
>>>>SCSI commands from one lld and send them to another lld instead of
>>>>sending them to user space.
>>>
>>>Although the approach of passing SCSI commands from a target LLD to an
>>>initiator one without any significant interventions from the target
>>>software looks to be nice and simple, you should realize how limited,
>>>unsafe and illegal it is, since it badly violates SCSI specs.
>>
>>I think that 'implemented cleanly' means that one scsi_host is assigned
>>to only one initiator.
> 
> Vladislav listed a number of issues that are inherent in an implementation
> that does not have a 1:1 relationship of initiators to targets.  The vscsi
> architecture defines the 1:1 relationship; it's imposible to have more
> than one initiator per target.

Just few small notes:

1. As I already wrote, complete 1:1 relationship isn't practically 
possible, because there is always a local access on the target (i.e. one 
more initiator) and you can't disable it on practice.

2. 1:1 relationship is a serious limitation for usage cases like an SPI 
tape library serving backup for several servers on an FC net.

Vlad