[Lustre-discuss] Reads Starved

Roger Spellman Roger.Spellman at terascala.com
Tue May 31 14:28:42 PDT 2011


Hi,

I am running a series of tests, and I am surprised by the results.


If I use about 10 clients, then the write performance of my system is 2
GB/s, and the read performance of my system is also 2 GB/s.  These are
the results when I run either reads or writes, but not both at the same
time.

 

But, when I have 10 clients doing reads, and a different 10 clients
doing writes, the write performance barely drops, but the read
performance drops to about 150 MB/s.

 

I am using the deadline scheduler.  I have played around with various
parameters, such as nr_requests, writes_starved, and fifo_batch, but
with little impact.  

 

Can anyone suggest why this is occurring, and how to address it?

In my idealized world, the read and write performance should be
proportional to the initial read and write performance, and the ratio of
the number of read and write clients.

 

Thanks.

 

Roger Spellman

Staff Engineer

Terascala, Inc.

508-588-1501

www.terascala.com http://www.terascala.com/

 

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