[Lustre-discuss] Bad read performance

Oleg Drokin Oleg.Drokin at Sun.COM
Thu Aug 20 19:57:46 PDT 2009


Hello!

    Any chance you can use more modern release like 1.8.1? There was a  
number of bugs fixed including some readahead-logic fixes that could  
impede read performance.

Bye,
     Oleg
On Aug 20, 2009, at 10:38 PM, Alvaro Aguilera wrote:

> Thanks for pointing that out. I was using the default striping,  
> which in my case is 1mb stripes, on one OST.
>
> However,  If I change the stripe size to 32mb (the size of the  
> buffers being written/read), the function used to write the file  
> using O_DIRECT stops working. Its code is very similar to the one  
> posted above and the problem is that the write()-function stucks  
> while writing the first buffer. Is there any trick for using  
> O_DIRECT in Lustre? I've aligned the buffer using posix_memalign(),  
> and every offset and count seem to be a multiple of the page-size  
> (4kb).
>
>
>
>
>
> On Fri, Aug 21, 2009 at 12:04 AM, Brian J. Murrell <Brian.Murrell at sun.com 
> > wrote:
> On Thu, 2009-08-20 at 23:52 +0200, Alvaro Aguilera wrote:
> > I'm facing the following problem: when this code is run in parallel
> > the read operations on certain processes start to need more and more
> > time to complete. I attached a graphical trace of this, when using
> > only 2 processes.
>
> Just a (perhaps silly) question, but does the striping of the file (or
> the directory the file is being created in) on the filesystem match  
> your
> I/O patterns?  That is, ideally, each thread/rank/process (whatever  
> you
> want to call them) should be doing I/O in it's own stripe.
>
> $ man lfs
>
> if none of this is meaningful.
>
> b.
>
>
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