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MapReduce, mail # user - HDFS HA IO Fencing


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Re: HDFS HA IO Fencing
Steve Loughran 2012-10-26, 17:23
On 26 October 2012 15:37, Todd Lipcon <[EMAIL PROTECTED]> wrote:

> NFS Locks typically last forever if you disconnect abruptly. So they are
> not sufficient -- your standby wouldn't be able to take over without manual
> intervention to remove the lock.

+1. This is why you are told to mount your shared edit log NFS servers with
the "soft" option -otherwise you can't swap over to the other machines.
see: http://www.faqs.org/docs/linux_network/x-087-2-nfs.mountd.html
>
> If you want to build an unreliable system that might corrupt your data,
> you could set up 'shell(/bin/true)' as a second fencing method. But, it's
> really a bad idea. There are failure scenarios which could cause split
> brain if you do this, and you'd very likely lose data
>

You could do it on a cluster where you were prepared to lose/corrupt all
the data. But in that world: why bother?