[lustre-discuss] Lustre client caching question

[John Bauer]

I have an application that reads a 70GB section of a file forwards and 
backwards multiple ( 14 ) times.  This is on a 64 GB system.  Monitoring 
/proc/meminfo  shows that the memory consumed by file cache bounces 
around the 32GB value.  The forward reads go at about 3.3GB/s.  What is 
disappointing is the backwards read performance.  One would think that 
after the file is read forwards the most recently used 32GB of the file 
should be in the system buffers and the reading of that the first 32GB 
of the file going backwards should be coming out of the system buffers.  
But the backwards reads generally perform at about 500MB/s.  Generally 
the first 1GB going backwards is at 5.5GB/s, but then the remaining 
backwards read is at the 500MB/s.

The Lustre client version is 2.12.9_ddn18.  The file is striped at 4x1M.

Is this expected behavior?

John