[lustre-discuss] Large file read performance degradation from multiple OST's

[Vicker, Darby (JSC-EG311)]

>> I tried a 2.8 client mounting the 2.9 servers and that showed the expected behavior ??? increasing 
>> performance with increasing OST's.  Two things:
>> 
>> 1.  Any pointers to compiling a 2.8 client on recent RHEL 7 kernels would be helpful.  I had to boot 
>>     into an older kernel to get the above test done.
>> 
>> 2. Any help to find the problem in the 2.9 code base would also be helpful.
>
> The fast_read feature has been added to the client-side read path between 2.8 and 2.9. So for starters it might
> be worthwhile to re-run the test on a 2.9 client with fast_read=0?

I've verified that the client compiled with the latest master branch code still reads very fast on 1 OST and slow multiple OSTs.  The behavior is the same with fast_read=0 (also with the master branch client).  We'll try to isolate the problem with a git bisect.