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From Michael Segel <michael_se...@hotmail.com>
Subject Re: Compactions nice to have features
Date Wed, 08 Oct 2014 19:30:29 GMT

On Oct 5, 2014, at 11:01 PM, lars hofhansl <larsh@apache.org> wrote:

>>> - rack IO throttle. We should add that to accommodate for over subscription at
the ToR level.
>> Can you decipher that, Lars?
> 
> ToR is "Top of Rack" switch. Over subscription means that a ToR switch usually does not
have enough bandwidth to serve traffic in and out of rack at full speed.
> For example if you had 40 machines in a rack with 1ge links each, and the ToR switch
has a 10ge uplink, you'd say the ToR switch is 4 to 1 over subsctribed.
> 
> 
> Was just trying to say: "Yeah, we need that" :)
> 


Hmmm. 

Rough math…  using 3.5” SATA II (7200 RPM) drives … 4 drives would max out 1GbE.  So
then  a server with 12 drives would max out 3Gb/S. Assuming 3.5” drives. 2.5” drives and
SATAIII would push this up. 
So in theory you could get 5Gb/S or more from a node. 

16 serves per rack… (again YMMV based on power, heat, etc … ) thats 48Gb/S and up. 

If you had 20 servers and they had smaller (2.5” drives) 5Gb/S x 20 = 100Gb/S. 

So what’s the width of the fabric?  (YMMV based on ToR) 

I don’t know why you’d want to ‘throttle’ because the limits of the ToR would throttle
you already. 

Of course I’m assuming that you’re running a M/R job that’s going full bore. 


Are you seeing this? 
I would imagine that you’d have a long running job maxing out the I/O and seeing a jump
in wait CPU over time.  

And what’s the core to spindle ratio? 



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