Yes, that is the scenario I think of. Queued commands seems to be the
right thing here. But which layer is responsible for determining
whether a particular SCSI command should be queued to the SCSI device and
which tag should be used? How does tagged queuing work in Linux?
Regards
Martin
On Mon, 24 Jul 2000 [EMAIL PROTECTED] wrote:
>
>
>
> I can not talk directly about select_queue_depths() and cmd_per_lun
> specifics, but yes, the protocol provides for command queueing in the
> LUN. Some large RAID devices utilize TCQ's of 80 or so. This allows
> the device to re-order the cmds for best performance (within limits).
>
> Multi-initiator in Linux is not that robust. It can work in SCSI, but it
> is also exposed to data corruption
> as the various hosts "fight" over who owns the bus and its devices. FC
> re-uses the SCSI
> middle layer driver.
>
> I've seen the function you describe refered to as data path optimization.
> A layer of code sits
> above the driver and routes commands to which ever adapter is least busy.
> If one path
> goes down, all traffic is then routed to the other path, providing
> redundancy as well.
>
> The other consideration in your scenario is the device itself. It has to
> support cmd queueing and
> would have to have multiple active ports.
>
> Regards,
> Steve Buller
> (std disclaimer: the comments above are my own and not those of my
> employer.)
>
>
> Martin Peschke <[EMAIL PROTECTED]>@vger.rutgers.edu on 07/24/2000
> 09:07:39 AM
>
> Sent by: [EMAIL PROTECTED]
>
>
> To: [EMAIL PROTECTED]
> cc:
> Subject: concurrent commands to same LUN ?
>
>
>
> I am just wondering about select_queue_depths() and cmd_per_lun.
> Is a HBA driver allowed to have more than one outstanding command at the
> same LUN? Or is it responsible for command serialization?
> I am just thinking about multiple paths in Fibre Channel environments
> because of several FC adapters within a single host connected to the same
> switched fabric. Are there cases where I can spread several commands to
> the same LUN over multiple ports at the same time to (maybe) increase
> performance?
> Thanks.
>
> Martin Peschke
>
>
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