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From "Pamecha, Abhishek" <apame...@x.com>
Subject Re: HDFS using SAN
Date Thu, 18 Oct 2012 15:18:10 GMT
Yes, I have been reaching the same conclusions here. Tom would you care to spell out the 'obvious'
io considerations? I would like to see if there are more that  are different than mine.

My  3 observations have been that
1. for full tables scan MR jobs, SAN approach is transporting entire dataset over the n/w
to data nodes. Not good.
2. The shuffle s actually includes more n/w transfers when it could have been just intra-SAN
transfer. Disadvantage.
3. SAN controller caches ( an additional stop in data transfer as opposed to das) may not
be utilized as effectively because they are shared by multiple data nodes. ( frequent eviction)

So overall my conclusion is MR is not the best suited data processing method when data is
stored in a SAN.

Btw, I thought SAN would do block level transfer and file system on top is your choice. I
was surprised to see GPFS 'as' the SAN. Could you please clarify?

Any way you can share your cluster size?


i Sent from my iPad with iMstakes

On Oct 18, 2012, at 7:41, "Tom Deutsch" <tdeutsch@us.ibm.com<mailto:tdeutsch@us.ibm.com>>

Agreed Luca, we do this to support existing customers that have requested it and it works
fine within obvious IO considerations. But not a recommended way to do a green field deployment.

Tom Deutsch
Program Director
Information Management
Big Data Technologies
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Costa Mesa, CA 92626-1420

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<graycol.gif>Luca Pireddu ---10/18/2012 05:33:48 AM---On 10/18/2012 02:21 AM, Pamecha,
Abhishek wrote: > Tom

From: Luca Pireddu <pireddu@crs4.it<mailto:pireddu@crs4.it>>
To: user@hadoop.apache.org<mailto:user@hadoop.apache.org>,
Date: 10/18/2012 05:33 AM
Subject: Re: HDFS using SAN


On 10/18/2012 02:21 AM, Pamecha, Abhishek wrote:
> Tom
> Do you mean you are using GPFS instead of HDFS? Also, if you can share,
> are you deploying it as DAS set up or a SAN?
> Thanks,
> Abhishek

Though I don't think I'd buy a SAN for a new Hadoop cluster, we have a
SAN and are using it *instead of HDFS* with a small/medium Hadoop
MapReduce cluster (up to 100 nodes or so, depending on our need).  We
still use the local node disks for intermediate data (mapred local
storage).  Although this set-up does limit our possibility to scale to a
large number of nodes, that's not a concern for us.  On the plus, we
gain the flexibility to be able to share our cluster with non-Hadoop
users at our centre.

Luca Pireddu
CRS4 - Distributed Computing Group
Loc. Pixina Manna Edificio 1
09010 Pula (CA), Italy
Tel: +39 0709250452

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