[Gluster-users] GlusterFS on a two-node setup

Ramon Diaz-Uriarte rdiaz02 at gmail.com
Sun May 20 21:55:55 UTC 2012

On Sun, 20 May 2012 20:38:02 +0100,Brian Candler <B.Candler at pobox.com> wrote:
> On Sun, May 20, 2012 at 01:26:51AM +0200, Ramon Diaz-Uriarte wrote:
> > Questions:
> > ==========
> > 
> > 1. Is using GlusterFS an overkill? (I guess the alternative would be to use
> >   NFS from one of the nodes to the other)

> In my opinion, the other main option you should be looking at is DRBD
> (www.drbd.org).  This works at the block level, unlike glusterfs which works
> at the file level.  Using this you can mirror your disk remotely.

Brian, thanks for your reply. 

I might have to look at DRBD more carefully, but I do not think it fits my
needs: I need both nodes to be working (and thus doing I/O) at the same
time. These are basically number crunching nodes and data needs to be
accessible from both nodes (e.g., some jobs will use MPI over the
CPUs/cores of both nodes ---assuming both nodes are up, of course ;-).

> If you are doing virtualisation then look at Ganeti: this is an environment
> which combines LVM plus DRBD and allows you to run VMs on either node and
> live-migrate them from one to the other.
> http://docs.ganeti.org/ganeti/current/html/

I am not doing virtualisation. I should have said that explicitly. 

> If a node fails, you just restart the VMs on the other node and away you go.

> > 2. I plan on using a dedicated partition from each node as a brick. Should
> >   I use replicated or distributed volumes?

> A distributed volume will only increase the size of storage available (e.g. 
> combining two 600GB drives into one 1.2GB volume - as long as no single file
> is too large).  If this is all you need, you'd probably be better off buying
> bigger disks in the first place.

> A replicated volume allows you to have a copy of every file on both nodes
> simultaneously, kept in sync in real time, and gives you resilience against
> one of the nodes failing.

But from the docs and the mailing list I get the impression that
replication has severe performance penalties when writing and some
penalties when reading. And with a two-node setup, it is unclear to me
that, even with replication, if one node fails, gluster will continue to
work (i.e., the other node will continue to work). I've not been able to
find what is the recommended procedure to continue working, with
replicated volumes, when one of the two nodes fails. So that is why I am
wondering what would replication really give me in this case.



> Regards,

> Brian.
Ramon Diaz-Uriarte
Department of Biochemistry, Lab B-25
Facultad de Medicina 
Universidad Autónoma de Madrid 
Arzobispo Morcillo, 4
28029 Madrid

Phone: +34-91-497-2412

Email: rdiaz02 at gmail.com
       ramon.diaz at iib.uam.es


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