[gpfsug-discuss] Baseline testing GPFS with gpfsperf

valdis.kletnieks at vt.edu valdis.kletnieks at vt.edu
Wed Jul 26 00:59:08 BST 2017


On Tue, 25 Jul 2017 15:46:45 -0500, "Scott C Batchelder" said:

> - Should the number of threads equal the number of NSDs for the file
> system? or equal to the number of nodes?

Depends on what definition of "throughput" you are interested in. If your
configuration has 50 clients banging on 5 NSD servers, your numbers for 5
threads and 50 threads are going to tell you subtly different things...

(Basically, one thread per NSD is going to tell you the maximum that
one client can expect to get with little to no contention, while one
per client will tell you about the maximum *aggregate* that all 50
can get together - which is probably still giving each individual client
less throughput than one-to-one....)

We usually test with "exactly one thread total", "one thread per server",
and "keep piling the clients on till the total number doesn't get any bigger".

Also be aware that it only gives you insight to your workload performance if
your workload is comprised of large file access - if your users are actually
doing a lot of medium or small files, that changes the results dramatically
as you end up possibly pounding on metadata more than the actual data....
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