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

[Mike Christie <michael.christie@oracle.com>]

On 10/19/20 1:55 PM, Muneendra Kumar M wrote:
> Hi Micheal,
> AFIK As long as the paths are available irrespective of  the path is moved
> to marginal path group or not multipathd  will keep sending the send path
> tester IO (TUR) to check the health status.
> 

You can change the multipathd code.


> Benjamin,
> Please let me know if iam wrong >
> Regards,
> Muneendra.
> 
> 
> -----Original Message-----
> From: Mike Christie [mailto:michael.christie@oracle.com]
> Sent: Tuesday, October 20, 2020 12:15 AM
> To: Muneendra Kumar M <muneendra.kumar@broadcom.com>; Hannes Reinecke
> <hare@suse.de>
> Cc: linux-scsi@vger.kernel.org; jsmart2021@gmail.com; emilne@redhat.com;
> mkumar@redhat.com
> Subject: Re: [PATCH v3 05/17] scsi_transport_fc: Added a new rport state
> FC_PORTSTATE_MARGINAL
> 
> On 10/19/20 1:03 PM, Muneendra Kumar M wrote:
>> 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.
> 
> 
> If your daemon works such that you only move paths from marginal to active
> if you get an ELS indicating the path is ok or you get a link up, then why
> have multipathd send path tester IO to the paths in the marginal path group?
> They do not do anything do they?
> 
> 
> 
>> 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.
>>