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

[Philipp Reisner]

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
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: Dipl-Ing Philipp Reisner
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