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From Arun C Murthy <ar...@yahoo-inc.com>
Subject Re: Hadoop Java Versions
Date Tue, 28 Jun 2011 17:25:05 GMT
We at Yahoo are about to deploy code to ensure a disk failure on a datanode is just that -
a disk failure. Not a node failure. This really helps avoid replication storms.

It's in the 0.20.204 branch for the curious.


Sent from my iPhone

On Jun 28, 2011, at 3:01 AM, "Steve Loughran" <stevel@apache.org> wrote:

> On 28/06/11 04:49, Segel, Mike wrote:
>> Hmmm. I could have sworn there was a background balancing bandwidth limiter.
> There is, for the rebalancer, node outages are taken more seriously, 
> though there have been problems in past 0.20.x where there was a risk of 
> a cascade failure on a big switch/rack failure. The risk has been 
> reduced, though we all await field reports to confirm this :)
> You can get 12-24 TB in a server today, which means the loss of a server 
> generates a lot of traffic -which argues for 10 Gbe.
> But
>  -big increase in switch cost, especially if you (CoI warning) go with 
> Cisco
>  -there have been problems with things like BIOS PXE and lights out 
> management on 10 Gbe -probably due to the NICs being things the BIOS 
> wasn't expecting and off the mainboard. This should improve.
>  -I don't know how well linux works with ether that fast (field reports 
> useful)
>  -the big threat is still ToR switch failure, as that will trigger a 
> re-replication of every block in the rack.
> 2x1 Gbe lets you have redundant switches, albeit at the price of more 
> wiring, more things to go wrong with the wiring, etc.
> The other thing to consider is how well the "enterprise" switches work 
> in this world -with a Hadoop cluster you can really test those claims 
> how well the switches handle every port lighting up at full rate. 
> Indeed, I recommend that as part of your acceptance tests for the switch.

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