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From Jean-Daniel Cryans <jdcry...@apache.org>
Subject Re: Zookeeper quorum config
Date Thu, 09 Dec 2010 17:13:25 GMT
Really, for 5 nodes, the master is your SPOF, so unless you plan to
use ZK for anything else then it's probably going to be easier/faster
to have only 1 ZK server. Collocating ZK and region servers is risky
if ZK doesn't have it's own disk, doing it 3 times is 3 times worse :)

Also it may save you a few hours of debugging weird issues.

J-D

On Thu, Dec 9, 2010 at 1:49 AM, Hari Sreekumar <hsreekumar@clickable.com> wrote:
> I have master also serving as regionserver. I'll run ZK also on 3 of the
> regionservers. I don't have too much data (few TBs only), so I guess it
> would be fine?
>
>
> On Thu, Dec 9, 2010 at 12:44 AM, Ted Dunning <tdunning@maprtech.com> wrote:
>
>> 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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