[Lustre-discuss] Performance Drop creating big files

Jason Rappleye jason.rappleye at nasa.gov
Sat May 31 00:18:40 PDT 2008


Hi Roger,

This sounds terribly familiar. The likely cause can be found by  
reading through the following thread:

http://lists.lustre.org/pipermail/lustre-discuss/2008-March/007024.html

Note that running dumpe2fs on each device, as suggested by one of the  
messages in the thread, did *not* result in a performance improvement.

j

On May 30, 2008, at 1:25 PM, Roger Spellman wrote:

> I am seeing the following odd behavior.  I have several OSSes, each  
> with a 7T RAID 5.
>
>
>
> If I use a single client to create a single 1T file which is  
> striped to a single OST, the performance starts off at about 400 MB/ 
> s (which is typical for my HW), then gradually decreases, until it  
> reaches 250 MB/s.  I’ve seen this with both IOZone and dd.
>
>
> As an experiment, I wrote a script that creates two hundred 10G  
> files, without removing them.  Again, the performance starts off at  
> 400 MB/s.  But, the performance stays nearly the same throughout  
> the test.
>
>
>
> The only difference between these tests is that in the second case,  
> there are lots of opens & closes, and in the first case, just a  
> single open and close.
>
>
>
> Can anyone explain what is happening here, and how to possible fix it?
>
>
>
> Thanks.
>
>
>
> Roger Spellman
>
> Sr. Staff Engineer
>
> Terascala, Inc.
>
>
>
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--
Jason Rappleye
System Administrator
NASA Advanced Supercomputing Division
NASA Ames Research Center
Moffett Field, CA 94035
jason.rappleye at nasa.gov







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