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From Adrian Hamza <adrian.ha...@hotmail.com>
Subject RE: Running zookeeper with journaling disabled on an ext4
Date Wed, 21 Oct 2015 19:44:28 GMT
No fsync can lead to data loss as the data could be written only in the OS cache but no on
the disk. We do use fsync to prevent that and we are not going to disable it.

> Date: Wed, 21 Oct 2015 14:00:57 -0400
> Subject: Re: Running zookeeper with journaling disabled on an ext4
> From: edward.capriolo@huffingtonpost.com
> To: user@zookeeper.apache.org
> 
> There used to be this setting in zk.
> 
> zookeeper.forceSync
> Using Kafka I used to set this setting to false, The reason is I had a
> number of clients writing offsets to zk and the disk system was always
> sync-ing dirty pages. The system would be super high IO wait.
> 
> I set this to false and disk usage basically dropped to 0.
> 
> On Wed, Oct 21, 2015 at 1:47 PM, Ivan Kelly <ivank@apache.org> wrote:
> 
> > >
> > > What's your opinion on running Zookeeper with file system journaling
> > > disabled on an EXT4 file system?
> > > We need every ounce of performance out of it, and I believe given the
> > > Zookeeper implementation (operations are logged, majority quorum is
> > > required for succeeding, checkpoints are swapped only after being
> > complete)
> > > I feel that EXT4 journaling is redundant. Disabling EXT4 journaling could
> > > improve performance. We have 5 servers in a Zookeeper ensemble. Am I
> > > missing something or this should be fine?
> >
> > I would recommend against it. With ext4 journalling disabled, a server
> > crash will likely lose data, unless you have all write caching disabled. If
> > you have all write caching disabled, I'd expect to see worse performance
> > for all applications. It's not much safer than running in a ramdisk.
> >
> > -Ivan
> >
 		 	   		  
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