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From stephen mulcahy <stephen.mulc...@deri.org>
Subject Re: Hadoop performance - xfs and ext4
Date Tue, 11 May 2010 14:33:30 GMT
On 23/04/10 15:43, Todd Lipcon wrote:
> Hi Stephen,
>
> Can you try mounting ext4 with the nodelalloc option? I've seen the same
> improvement due to delayed allocation butbeen a little nervous about that
> option (especially in the NN where we currently follow what the kernel
> people call an antipattern for image rotation).

Hi Todd,

Sorry for the delayed response - I had to wait for another test window 
before trying this out.

To clarify, my namename and secondary namenode have been using ext4 in 
all tests - reconfiguring the datanodes is a fast operation, the nn and 
2nn less so. I figure any big performance benefit would appear on the 
data nodes anyway and can then apply it back to the nn and 2nn if 
testing shows any benefits in changing.

So I tried running our datanodes with their ext4 filesystems mounted 
using "noatime,nodelalloc" and after 6 runs of the TeraSort, it seems it 
runs SLOWER with those options by between 5-8%. The TeraGen itself 
seemed to run about 5% faster but it was only a single run so I'm not 
sure how reliable that is.

hth,

-stephen

-- 
Stephen Mulcahy, DI2, Digital Enterprise Research Institute,
NUI Galway, IDA Business Park, Lower Dangan, Galway, Ireland
http://di2.deri.ie    http://webstar.deri.ie    http://sindice.com

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