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From Todd Lipcon <t...@cloudera.com>
Subject Re: HDFS Read ThroughPut and DISK Read ThroughPut
Date Fri, 14 May 2010 17:02:30 GMT
Hi Rohan,

How are you measuring throughput? The throughput from a single client will
not scale up as the cluster size increases, as it does not parallelize reads
across multiple nodes. Of course it will also be limited by the inbound
bandwidth of that node.


On Fri, May 14, 2010 at 1:23 AM, Rohan Rai <rohan.rai@inmobi.com> wrote:

> Hi
> Is there a relationship between HDFS Read throught put and Disk Read
> throughput.
> If yes what would be that.
> Lets say we have a disk giving us 120 MB/s
> And a Cluster of 6 Nodes
> Each Node having 6 disk.
> So in an absolutely ideal world it should give us a through put
> of 120*6*6 MB/s if used in parallel
> In a non ideal world we can divide above by a factor of x
> Then why is that the general CLUSTER read throughput is so very less.
> Generally it hovers around 90MB/s.
> How is the throughput which cluster provides is accounted for.
> Just for information, configs are , 8 GB RAM, 250 GB HDD, 8 Maps per
> node, 128 Kb Block size
> Regards
> Rohan
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Todd Lipcon
Software Engineer, Cloudera

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