1. path_latencty_monitor and path_latency_threshold are simply audit logs, extra logging that PowerPath provides to assist with identifying performance issues on a host, they do not influence failover in any way.
2. The trigger that causes PowerPath to failover is usually the HBA timeout value, for example, with Emulex HBA's the value lpfc_nodev_tmo=10 Specifies the amount of time [0-255] that all I/O errors will be held by the HBA driver on devices that disappear. For PowerPath we recommend a value of 10 seconds. After 10 seconds the HBA driver reports to PP that the device has not responded, and PowerPath will then take action and re-route the IO to the alternate path. QLogic have similar parameters, please see the QLogic and Emulex documentation for your HBA/Driver combination.
Conor
341 Posts
0
November 21st, 2008 03:00
1. path_latencty_monitor and path_latency_threshold are simply audit logs, extra logging that PowerPath provides to assist with identifying performance issues on a host, they do not influence failover in any way.
2. The trigger that causes PowerPath to failover is usually the HBA timeout value, for example, with Emulex HBA's the value lpfc_nodev_tmo=10 Specifies the amount of time [0-255] that all I/O errors will be held by the HBA driver on devices that disappear. For PowerPath we recommend a value of 10 seconds.
After 10 seconds the HBA driver reports to PP that the device has not responded, and PowerPath will then take action and re-route the IO to the alternate path.
QLogic have similar parameters, please see the QLogic and Emulex documentation for your HBA/Driver combination.
Conor
341 Posts
0
December 15th, 2008 02:00
Conor