[Linux-cluster] GNBD vs DRBD to mirror two disks via the network

[Kaloyan Kovachev]

On Mon, 13 Jul 2009 16:03:00 +0100, Bryn M. Reeves wrote
> On Mon, 2009-07-13 at 15:40 +0100, Bushby, Bruce (London)(c) wrote:
> >  
> > Greetings!
> >  
> > I'm hoping a member could assist me in clearing up some understanding
> > I appear to be missing when it comes to GNBD.
> >  
> > Today I clustered two vmware machines (active/passive shared nothing)
> > and then configure GNBD....thats when I noticed it
> > wants to "export" a device from one node and "import" the device on
> > the other node...which I did and it all works....but that is
> > not what I was after.
> >  
> > Can GNBD be configured to keep two disks on different systems in sync
> > using both synchronous and asynchronous write options?
> 
> No. GNBD is just a cluster-aware network block device (i.e. it
> implements fencing so that we can cut off a failing node from the shared
> storage).
> 
> It's only useful if you want shared storage for e.g. GFS but don't have
> access to hardware shared storage resources (or only have shared storage
> hardware on a subset of nodes and want to spread that out to more nodes
> using IP).
> 

and a question from me here (asked a week ago but with no answer, so will try
to be more clear now).

'only have shared storage hardware on a subset of nodes ...' - OK so if we
have 3 nodes and 2 of them have access to the storage and are exporting it via
GNBD - how the 3-rd node may access the data from both of them and not
interupting the services in case of failure of either of the first two?

> Regards,
> Bryn.
> 
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