Rkierski: Created page with "The number of tasks or processes used in a test will impact the measured performance in many ways. * Each IO request will have some period of time where the request is in-fli..."

2015-02-20T20:52:27Z

Created page with "The number of tasks or processes used in a test will impact the measured performance in many ways. * Each IO request will have some period of time where the request is in-fli..."

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The number of tasks or processes used in a test will impact the measured performance in many ways.

* Each IO request will have some period of time where the request is in-flight. While one process is waiting for that IO to complete, another process can be forming it's own IO requests. This makes better use of the CPU and other system resources.
* IO requests from different process that overlap may cause lock contention both locally and on the MDS and OSS. Lock contention will cause an increase in IO latency.

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Depending on your usage of IOR and filesystem striping, IOR may assign IO offsets such that different processes on the same client are sending requests to different OSS and/or OST's. If the total number of processes (client-node-count * processes-per-client) is evenly divisible by the number of OST's, it's likely that each process will only communicate with one OST and therefore only one OSS.

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The goal in choosing a task count is to generate enough IO's to keep the network interfaces busy. If you choose a task count that is too high, IO latency and CPU utilization will increase without seeing an increase in throughput.

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[[This]] is a page that talks about the filesystem tunables that control the number of RPCs and the amount of memory each client can have outstanding at any time.

HeroRunTaskCount - Revision history

Rkierski: Created page with "The number of tasks or processes used in a test will impact the measured performance in many ways. * Each IO request will have some period of time where the request is in-fli..."