PowerPath and I/O Threads

Question

I'm wondering during a troubleshooting exercise on a Windows host how PowerPath handles single threaded and multi threaded applications and their I/O. If a single thread batch file were to kick off some I/O requests to the SAN, will the load-balancing features of PP 'manage' that thread across a single link if there is heavy I/O across both paths, or will it balance it regardless of application behavior?

Collier2 · Answer

When PowerPath is installed, applications access the PowerPath filter driver, not the HBA driver. Given this, if you have the fully licensed version installed, for all I/Os, PowerPath looks at the volume path set and determines the path for the I/O based on the load balancing policy and failover settings. I would assume the same to be true regardless if the application single or multi threaded.

AranH1 · Answer

Whether the application is multi-threaded or not will be irrelevant to a fully licensed installation of PowerPath that has load balancing enabled. PowerPath will load balance ALL i/o requests to the logical disks that are presented to the host OS.

DA · Answer

You may get a better performance by using non-default load-balancing policy, such as Round Robin (rr), Least I/O (li) or Least Blocks (lb). Best is to test performance with each of the above since the results will always depend on your I/O profile (and no environment is the same).

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PowerPath and I/O Threads

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