[dm-devel] LSF: Multipathing and path checking question

[Hannes Reinecke]

Mike Christie wrote:
> Mike Christie wrote:
>>> For starters we just should send a netlink event when fast_fail_io has
>>> fired. We could easily integrate that one in multipathd and would gain
>>> an instant benefit from that as we can switch paths in advance.
>>> Next step would be to implement an additional sdev state which would
>>> return 'DID_TRANSPORT_FASTFAIL' for any 'normal' I/O; it would be
>>> inserted between 'RUNNING' and 'CANCEL'.
>>> Transition would be possible between 'RUNNING' and 'FASTFAIL', but
>>> it would only be possible to transition into 'CANCEL' from 'FASTFAIL'.
>>>
>>
>>
>> Yeah, a new sdev state might be nice. Right now this state is handled
>> by the classes. For iscsi and FC the port/session will be in
>> blocked/ISCSI_SESSION_FAILED. Then internally the classes are
>> decieding what to do with IO in the *_chkready functions.
>>
>>
> 
> 
> How about setting the device to the offline state for this case where
> fast_io_fail has fired but the dev_loss_tmo has not yet fired? As fast
> as failing IO we get the same result. scsi-ml would fail the incoming IO
> instead of it getting to the class _chkready functions, but the scsi
> device state indicates that it cannot execute IO which might be nice for
> users.
> 
Ah, no. OFFLINE is a dead end status out of which we cannot transition
from inside the kernel. I'd prefer a new state here.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
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