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Hadoop, mail # user - risks of using Hadoop


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RE: risks of using Hadoop
Michael Segel 2011-09-18, 02:37

Gee Tom,
No disrespect, but I don't believe you have any personal practical experience in designing and building out clusters or putting them to the test.

Now to the points that Brian raised..

1) SPOF... it sounds great on paper. Some FUD to scare someone away from Hadoop. But in reality... you can mitigate your risks by setting up raid on your NN/HM node. You can also NFS mount a copy to your SN (or whatever they're calling it these days...) Or you can go to MapR which has redesigned HDFS which removes this problem. But with your Apache Hadoop or Cloudera's release, losing your NN is rare. Yes it can happen, but not your greatest risk. (Not by a long shot)

2) Data Loss.
You can mitigate this as well. Do I need to go through all of the options and DR/BCP planning? Sure there's always a chance that you have some Luser who does something brain dead. This is true of all databases and systems. (I know I can probably recount some of IBM's Informix and DB2 having data loss issues. But that's a topic for another time. ;-)

I can't speak for Brian, but I don't think he's trivializing it. In fact I think he's doing a fine job of level setting expectations.

And if you talk to Ted Dunning of MapR, I'm sure he'll point out that their current release does address points 3 and 4 again making their risks moot. (At least if you're using MapR)

-Mike
> Subject: Re: risks of using Hadoop
> From: [EMAIL PROTECTED]
> Date: Sat, 17 Sep 2011 17:38:27 -0600
> To: [EMAIL PROTECTED]
>
> I disagree Brian - data loss and system down time (both potentially non-trival) should not be taken lightly. Use cases and thus availability requirements do vary, but I would not encourage anyone to shrug them off as "overblown", especially as Hadoop become more production oriented in utilization.
>
> ---------------------------------------
> Sent from my Blackberry so please excuse typing and spelling errors.
>
>
> ----- Original Message -----
> From: Brian Bockelman [[EMAIL PROTECTED]]
> Sent: 09/17/2011 05:11 PM EST
> To: [EMAIL PROTECTED]
> Subject: Re: risks of using Hadoop
>
>
>
>
> On Sep 16, 2011, at 11:08 PM, Uma Maheswara Rao G 72686 wrote:
>
> > Hi Kobina,
> >
> > Some experiences which may helpful for you with respective to DFS.
> >
> > 1. Selecting the correct version.
> >    I will recommend to use 0.20X version. This is pretty stable version and all other organizations prefers it. Well tested as well.
> > Dont go for 21 version.This version is not a stable version.This is risk.
> >
> > 2. You should perform thorough test with your customer operations.
> >  (of-course you will do this :-))
> >
> > 3. 0.20x version has the problem of SPOF.
> >   If NameNode goes down you will loose the data.One way of recovering is by using the secondaryNameNode.You can recover the data till last checkpoint.But here manual intervention is required.
> > In latest trunk SPOF will be addressed bu HDFS-1623.
> >
> > 4. 0.20x NameNodes can not scale. Federation changes included in latest versions. ( i think in 22). this may not be the problem for your cluster. But please consider this aspect as well.
> >
>
> With respect to (3) and (4) - these are often completely overblown for many Hadoop use cases.  If you use Hadoop as originally designed (large scale batch data processing), these likely don't matter.
>
> If you're looking at some of the newer use cases (low latency stuff or time-critical processing), or if you architect your solution poorly (lots of small files), these issues become relevant.  Another case where I see folks get frustrated is using Hadoop as a "plain old batch system"; for non-data workflows, it doesn't measure up against specialized systems.
>
> You really want to make sure that Hadoop is the best tool for your job.
>
> Brian