Linux multipath (device-mapper) optimizations with 3par storage

Earlier this year we bought a 6-node 3par v800 array and it was being deployed with Oracle RAC Clusters running OEL 6.x.

We discovered that 3par's default configuration for multipath.conf would yield a 30 second I/O stall whenever we failed one of the paths.

Eventually  we were able to get support to offer adding "dev_loss_tmo            1" to the multipath.conf as such:

 defaults {  
  user_friendly_names yes  
  polling_interval    5  
  dev_loss_tmo      1  
 }  

With that in place, we would only observe a 1 second I/O stall during a path failure.