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From Brian Bockelman <bbock...@cse.unl.edu>
Subject Re: Mounting HDFS as local file system
Date Thu, 02 Dec 2010 17:24:54 GMT

On Dec 2, 2010, at 9:22 AM, Mark Kerzner wrote:

> Brian,
> 
> that almost answers my question. Still, are you saying that the problem of
> "Hadoop hates small files" does not exist?
> 

Well, I'd say "hates" is too strong of a word.  Several of the "costs" (NN memory, latency,
efficiency) in HDFS are a function of the number of files, and one needs to plan appropriately.
 Some  users can accept this fact and work with it; other, less sophisticated, users simply
need to be told "don't save anything less than 10MB".

Over Thanksgiving holidays, we had a process go awry and write 900,000 files smaller than
a kilobyte into one XFS directory.  This was definitely costly in system resources and inefficient,
but I wouldn't say XFS hates small files.

So you need to keep file size costs in your planning.  If you ignore this variable, you will
likely be bitten by these issues.

Brian


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