[Lustre-discuss] Performance Drop creating big files

[Roger Spellman]

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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