RE: [PATCH v3 05/17] scsi_transport_fc: Added a new rport state FC_PORTSTATE_MARGINAL

[Muneendra Kumar M <muneendra.kumar@broadcom.com>]

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Hi Michael,
Regarding the TUR (Test Unit Ready)command which I was mentioning .
Multipath daemon issues TUR commands on a regular intervals to check the
path status.
When a port_state is set to marginal we are not suppose to end up failing
the cmd  with DID_TRANSPORT_MARGINAL with out proceeding it.
This may  leads to give wrong health status.
Hannes/James Correct me if this is wrong.

Regards,
Muneendra.

-----Original Message-----
From: Muneendra Kumar M [mailto:muneendra.kumar@broadcom.com]
Sent: Monday, October 19, 2020 11:01 PM
To: 'Hannes Reinecke' <hare@suse.de>; 'Michael Christie'
<michael.christie@oracle.com>
Cc: 'linux-scsi@vger.kernel.org' <linux-scsi@vger.kernel.org>;
'jsmart2021@gmail.com' <jsmart2021@gmail.com>; 'emilne@redhat.com'
<emilne@redhat.com>; 'mkumar@redhat.com' <mkumar@redhat.com>
Subject: RE: [PATCH v3 05/17] scsi_transport_fc: Added a new rport state
FC_PORTSTATE_MARGINAL

Hi Michael,


>
>
> Oh yeah, to be clear I meant why try to send it on the marginal path
> when you are setting up the path groups so they are not used and only the
> optimal paths are used.
> When the driver/scsi layer fails the IO then the multipath layer will
> make sure it goes on a optimal path right so you do not have to worry
> about hitting a cmd timeout and firing off the scsi eh.
>
> However, one other question I had though, is are you setting up
> multipathd so the marginal paths are used if the optimal ones were to
> fail (like the optimal paths hit a link down, dev_loss_tmo or
> fast_io_fail fires, etc) or will they be treated like failed paths?
>
> So could you end up with 3 groups:
>
> 1. Active optimal paths
> 2. Marginal
> 3. failed
>
> If the paths in 1 move to 3, then does multipathd handle it like a all
> paths down or does multipathd switch to #2?
>
>Actually, marginal path work similar to the ALUA non-optimized state.
>Yes, the system can sent I/O to it, but it'd be preferable for the I/O to
>be moved somewhere else.
>If there is no other path (or no better path), yeah, tough.

>Hence the answer would be 2)


[Muneendra]As Hannes mentioned if there are no active paths, the marginal
paths will be moved to normal and the system will send the io.

Regards,
Muneendra.

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