Hi KC,  The SCSI inquiry command normally has a much lower timeout value than regular IOs, so the inquiry would timeout and fail much faster. Also, PowerPath path tests are scheduled every 10 seconds.  You can find documents about the specific values in the HBA drivers release notes/user guide.  Javier Soriano PowerPath Corporate Systems Engineer
Hi guys,  These days, while I'm support a customer, an issue confuses me a lot is hit as below:  1. A Linux server with a HBA which has 2 x 8G FC ports is zoned to two FAs of a Symmetrix array; 2. Shutdown the FC switch port one of the FC ports attached to while heavy IO traffic is flowing; 3. A IO pause will be triggered, during this time slot, no traffic can be delivered; 4. After a couple of seconds, the IO traffic gets redirected to those active paths.  After an investigation, some experts told me that 30 ~ 45 seconds will be taken normally in such situation before IO gets resume. The reason is PP needs to wait for IO failure return before it redirects IO, and scsi & hba driver have their own mechanism for retry which take times.  After some more investigation, where this 45 is from is clear:  # cat /sys/class/fc_remote_ports/rport-4:0-1/dev_loss_tmo 45  dev_loss_tmo - Specify the number of seconds the scsi layer will wait after a problem has been detected on a FC remote port before removing it from the system. It will be automatically adjusted to the overall retry interval no_path_retry * polling_interval if a number of retries is given with no_path_retry and the overall retry interval is longer than the specified dev_loss_tmo value.  But below questions confuse me: 1. Where is the 30 from? I have found that a bus test will be performed in a 30 seconds base periodically, is that where it is from? 2. In the failover white paper, a failed path(and its shared common setup such as all paths through the same bus) will be marked for test immediately, does it means the test will be triggered right after the marking or we still need to wait for the path test per its periodical setup? 3. Will the path test rely on scsi/hba retry mechanism? * If that is true, 30 seconds is definitely not enough at all since we still need to wait for the dev_loss_tmo; * If that is not true, does it means the test will be covered through other active paths by querying related storage array directly? It really confuses me a lot:(  Waiting for a clear explanation......, thanks:)
How long exactly PP will take to redirect failed IOs and why?