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From "Anthony Ikeda" <Anthony.Ik...@cardlink.com.au>
Subject RE: Active-Active Performance
Date Tue, 25 May 2010 02:28:56 GMT
Sorry Hemantha, internal terminology :)

We will most likely have 2 data centres (Site A and Site B) and we need data to be available
between the 2 sites, i.e., if Site A stores data, Site B must be able to read it pretty much
straight away.

We are thinking of installing Hadoop and HBase on each Site to ensure data stored at Site
A is readily available for Site B. We are not sure how many installations are required per
site yet but I'm guessing one site will house the Master the other the Slave.

Because this is an Active-Active configuration, we need to ensure that if the link between
each site goes down, they can still operate to a degree and once the link is recovered, both
sites will sync up once more.

Also from a maintenance point of view, we may wish to add more instances of Hadoop/HBase slaves
on new machines in each site without disturbing the operation of the application.

Anthony

-----Original Message-----
From: Hemanth Yamijala [mailto:yhemanth@gmail.com] 
Sent: Tuesday, 25 May 2010 12:19 PM
To: general@hadoop.apache.org
Subject: Re: Active-Active Performance

Anthony,

> In regards to different locations of the HADOOP home this is low
> priority more for testing not production. I was trying to install HADOOP
> for testing over 2 machines with only a Windows XP machine running
> Cygwin and a Mac running Darwin. Not a priority.
>
> In regards to my last question about operating in a detached fashion, we
> are trying to factor in what happens when the link between both sites is
> cut. Will both sites operate independently until the connection is
> re-established? Is there any particular setup required to ensure we can
> cover this scenario or is it an out-of-the-box feature?

When you say 'sites', do you mean two different Hadoop installations ?
In general, each site is independent. So, I am unable to understand
where the link comes in.


>
> Anthony
>
>
> -----Original Message-----
> From: Hemanth Yamijala [mailto:yhemanth@gmail.com]
> Sent: Tuesday, 25 May 2010 12:08 PM
> To: general@hadoop.apache.org
> Subject: Re: Active-Active Performance
>
> Anthony,
>
> I'm new to Hadoop and I've been given the task to see how we might
> utilise
>> Hadoop and HBase to implement an Active-Active site layer for sharing
>> information across a distributed application.
>>
>>
>>
>> I've been able to:
>>
>> *         Install and get Hadoop running on a single node and am in
> the
>> process of configure a 2 node setup.
>>
>> *         Install HBase on a single node and create a table and
> mapping as
>> well as insert data into the system
>>
>>
>>
>> Once I've got the mutli-node configured I hope to run some tests as
> well.
>>
>>
>>
>> I've noticed that trying to start Hadoop in distributed mode, the
> slave
>> will ssh to the master to start it as well (bin/start-all.sh) provided
> the
>> same path is setup on the remote machine.
>>
>>
>>
>> Questions:
>>
>> Can I configure the system IF the Hadoop installation is not in the
> same
>> location per machine?
>>
>
> I would think configuring and managing such a system would get very
> complex
> - for e.g. if you'll want to add nodes to expand in future. You would
> also
> not be able to take advantage of the very helpful scripts that come with
> Hadoop. Is there a reason why you want to do this ?
>
>> If the master node goes down (say due to electrical fault or system
> fault)
>> how do the slave nodes react? Will they continue to run? Will the
> nodes be
>> back in sync once the master starts again?
>>
>
> Hadoop slaves will continue. They will enter a retry loop trying to
> connect
> to the master until it comes up. In doing so, they could fill up log
> files
> very fast though. If the master starts with the same configuration,
> (same
> host, ports), they should be able to connect and resume.
>
>> Would I require a particular configuration to ensure that both our
> sites
>> can operate within the cluster as well as in a detached fashion (due
> to
>> maintenance or network issues)?
>>
>>
>>
> I did not quite follow this. Can you explain a little more about how you
> want to setup your system ?
>
> Thanks
> Hemanth
>
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