[dm-devel] multibus / failover and EMC CX600

[Mike Christie]

Tore Anderson wrote:
> * Hannes Reinecke
> 
>> That's the dev_loss_tmo setting. Just increase it to something to
>> your liking.
> 
> Oh, sweet.  This knob won't affect how long the layer will hold I/O
> before failing it (like lpfc_nodev_tmo), I assume?  (I'm worried about
> it taking longer for dm-multipath to detect failed paths).
> 

With newer versions of lpfc you can set 
/sys/class/fc_rport/rportXYZ/fast_io_fail_tmo to a low value so that IO 
is failed quickly, and then set the dev_loss_tmo to a high value so the 
device is not removed quickly.

The only problem may be that there is a race where dm-multpiath could be 
queueing IO to the scsi layer while the scsi layer is reporting a 
failure. That IO that was getting queued will then sit in the scsi layer 
until dev_loss_tmo fires. That is fixed with this patchset
http://marc.info/?l=linux-scsi&m=117399843216280&w=2
but I never finished testing it out.