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

Ramon Diaz-Uriarte rdiaz02 at gmail.com
Sun May 20 22:43:00 UTC 2012

On Sun, 20 May 2012 18:09:47 -0400,David Coulson <david at davidcoulson.net> wrote:

> On 5/20/12 5:55 PM, Ramon Diaz-Uriarte wrote:
> > 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 ;-).
> DRBD will let you do read/write on both nodes, but it requires a 
> clustered filesystem such as GFS2 or OCFS2 on top of it. You are also 
> limited to a max of two nodes.

Aha, thanks. I wasn't aware of that. I'll have to look into that
option. But then, I keep adding layers (and also, I keep adding layers of
manuals to read) which brings me to your next answer:

> >
> > 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.

> Gluster doing replication requires writes to hit both nodes, which may 
> slow you down a lot if there is significant latency between the two. I 
> run a replicated configuration, and have had nodes down for extended 
> periods - Gluster will repair the missing data from the brick on the 
> failed node during self-heal, so it is transparent. I've never had to 
> shut down applications in order for gluster to fix something first.

That is neat: so Gluster with replication just works and there is nothing
special I need to do.

That is great, because the configuration is fairly straightforward. So
what would be the pros/cons compared to using DRBD + OCFS?  Will DRBD +
OCFS give me much better read and, specially, write performance? I am
using Infiniband (QDR; a Qlogic QLE7340 HCA card) so latency should not be
that bad. 

I think I am getting confused with the options, now that I thought I had
narrowed down the problem to a couple of possible choices (or maybe its
too late here, and I should go to sleep ;-).



> David
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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