Re: [LSF/MM TOPIC] iSCSI MQ adoption via MCS discussion

[Sagi Grimberg <sagig@dev.mellanox.co.il>]

On 1/8/2015 4:11 PM, Bart Van Assche wrote:
> On 01/08/15 14:45, Sagi Grimberg wrote:
>> Actually I started with that approach, but the independent connections
>> under a single session (I-T-Nexus) violates the command ordering
>> requirement. Plus, such a solution is specific to iSER...
>
> Hello Sagi,
>
> Which command ordering requirement are you referring to ? The Linux
> storage stack does not guarantee that block layer or SCSI commands will
> be processed in the same order as these commands have been submitted.
>

I was referring to the iSCSI session requirement. I initially thought of
an approach to maintain multiple iSER connections under a single session
but pretty soon I realized that preserving commands ordering this way
is not feasible. So independent iSER connections means independent
iSCSI sessions (each with a single connection). This is indeed another
choice, which we are clearly debating on...

I'm just wandering if we are not trying to force-fit this model. How
would this model look like? We will need to define another entity to
track and maintain the sessions and to allocate the scsi_host. Will that
be communicated to user-space? How will error recovery look like?

Sagi.