linux-kernel - Re: [PATCH 00/16] DRBD: a block device for HA clusters

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Date:	Tue, 5 May 2009 17:56:28 +0200
From:	Philipp Reisner <philipp.reisner@...bit.com>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	david@...g.hm, Willy Tarreau <w@....eu>,
	Bart Van Assche <bart.vanassche@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>,
	Greg KH <gregkh@...e.de>, Neil Brown <neilb@...e.de>,
	Sam Ravnborg <sam@...nborg.org>, Dave Jones <davej@...hat.com>,
	Nikanth Karthikesan <knikanth@...e.de>,
	"Lars Marowsky-Bree" <lmb@...e.de>,
	Kyle Moffett <kyle@...fetthome.net>,
	Lars Ellenberg <lars.ellenberg@...bit.com>
Subject: Re: [PATCH 00/16] DRBD: a block device for HA clusters

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
: http://www.linbit.com

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