support explicitly placing files on specific Lustre OSTs

[glennklockwood]

I propose a feature that allows users to restrict IOR to only a specific list of Lustre OSTs for a variety of reasons related to file-per-process, e.g.,

1. I know that one OST is failed over and only achieves half performance, so the best performance is achieve by excluding the overloaded OSS
2. I want to test the performance of a single OST

I propose adding a new lustre-specific option, -O lustreosts that allows you to specify one or more OSTs using the same syntax as lfs setstripe -o, e.g.,

ior -F -O lustreosts=1 # restrict all files to ost0001
ior -F -O lustreosts=1-4 # restrict all files to ost0001-ost0004
ior -F -O lustreosts=0-267,270-299 # use all osts EXCEPT ost0268 and ost0269

This could be combined with -O lustrestripecount to stripe all file(s) across subsets of the osts specified using -O lustreosts. For example the following would create a file-per-process with each file striped over two OSTs while avoiding striping any files on ost0268 and ost0269:

ior -F -O lustreosts=0-267,270-299 -O lustrestripecount=2

I implemented the above against a fork of ior-3.3 here that I'm developing for other reasons but if this seems useful to the broader community, I'll port it forward to master. This will require

• cleaning up the ifdef mess around supporting older lustre versions
• adding these new features to the test suite
• testing this code in combination with shared file
• adding documentation