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From: Philipp Reisner <philipp.reisner@linbit.com>
Organization: LINBIT
To: James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: Re: [PATCH 00/16] DRBD: a block device for HA clusters
Date: Tue, 5 May 2009 17:56:28 +0200
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Cc: david@lang.hm, Willy Tarreau <w@1wt.eu>,
       Bart Van Assche <bart.vanassche@gmail.com>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       Jens Axboe <jens.axboe@oracle.com>, Greg KH <gregkh@suse.de>,
       Neil Brown <neilb@suse.de>, Sam Ravnborg <sam@ravnborg.org>,
       Dave Jones <davej@redhat.com>, Nikanth Karthikesan <knikanth@suse.de>,
       "Lars Marowsky-Bree" <lmb@suse.de>, Kyle Moffett <kyle@moffetthome.net>,
       Lars Ellenberg <lars.ellenberg@linbit.com>
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On Tuesday 05 May 2009 16:09:45 James Bottomley wrote:
> On Tue, 2009-05-05 at 10:21 +0200, Philipp Reisner wrote:
> > > > When you do asynchronous replication, how do you ensure that implicit
> > > > write-after-write dependencies in the stream of writes you get from
> > > > the file system above, are not violated on the secondary ?
> > >
[...]
> > > The way nbd does it (in the updated tools is to use DIRECT_IO and
> > > fsync).
> >
[...]
> I think you'll find the dio/fsync method above actually does solve all
> of these issues (mainly because it enforces the semantics from top to
> bottom in the stack).  I agree one could use more elaborate semantics
> like you do for drbd, but since the simple ones worked efficiently for
> md/nbd, there didn't seem to be much point.
>

Do I get it right, that you enforce the exact same write order on the 
secondary node as the stream of writes was comming in on the primary?

Using either DIRECT_IO or fsync() calls ?

Is DIRECT_IO/fsync() enabled by default ?

-Phil
-- 
: Dipl-Ing Philipp Reisner
: LINBIT | Your Way to High Availability
: Tel: +43-1-8178292-50, Fax: +43-1-8178292-82
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