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From Ted Dunning <tdunn...@maprtech.com>
Subject Re: Zookeeper quorum config
Date Wed, 08 Dec 2010 19:14:09 GMT
Ahh... that is very much at the other end of the spectrum from what I am
used to.

Yes.  It would not be good to run ZK on a system where the disk is
essentially unavailable for
significant amounts of time.

On Wed, Dec 8, 2010 at 10:24 AM, Jean-Daniel Cryans <jdcryans@apache.org>wrote:

> Ted,
>
> Sorry, wrong choice of words, HBase will be unreliable. I'm referring
> to a situation where the session timeout is caused by a very slow
> quorum because, as I saw it happening before, the datanodes where
> pegging the disk(s) while being hammered by the region servers.
>
> J-D
>
> On Wed, Dec 8, 2010 at 10:20 AM, Ted Dunning <tdunning@maprtech.com>
> wrote:
> > This is a bit misleading.  ZK is always reliable regardless of disk
> latency.
> >  All that happens on a busy disk is that
> > you get longer latency for ZK transactions.  For a dedicated and
> > well-configured machine, you can have average
> > latency (including committing to disk) of about 7 ms.  For a
> multi-purpose
> > busy machine, you may see latencies
> > of 300 ms.
> >
> > Neither case will cause unreliable operation.
> >
> > On Wed, Dec 8, 2010 at 10:14 AM, Jean-Daniel Cryans <jdcryans@apache.org
> >wrote:
> >
> >> Basically, ZK simply needs the lowest latency to disk and network in
> >> order to work reliably. It's not CPU intensive, and it's only memory
> >> intensive if you are using tons of znodes (HBase doesn't).
> >>
> >
>

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