[Beowulf] High Performance for Large Database

Craig Tierney ctierney at hpti.com
Mon Nov 15 12:27:15 EST 2004


On Mon, 2004-11-15 at 06:26, Laurence Liew wrote:
> Hi
> 
> The current version of GFS have a 64 node limit.. something to do with 
> maximum number of connections thru a SAN switch.

I would suspect the problem is that GFS doesn't scale past
64 nodes.  There is no inherent limitation in Linux on the
size of a SAN (well, if there is, it is much larger than 64 nodes).
Other shared filesystems, like StorNEXT and CXFS, are limited 
to 128 nodes due to scalability reasons.

> 
> I believe the limit could be removed in RHEL v4.
> 
> BTW, GFS was built for enterprise and not specifically for HPC... the 
> use of SAN (all nodes need to be connected to a single SAN storage).. 
> may be a bottleneck...
> 
> I would still prefer the model of PVFS1/2 and Lustre where the data is 
> distributed amongst the compute nodes

You can do this, but does anyone do it?  I suspect that most
implementations are setup where the servers are not on the compute
nodes.  This provides for more consistent performance across
the cluster.  Also, are you going to install redundant storage in
all of your compute nodes so that you can build a FS across the
compute nodes?  Unless the FS is for scratch only, I don't want
to have to explain to the users why the system keeps losing their data. 
Even if you use some raid1 or raid5 ATA controllers in a 
few storage servers, you are going to be able to build a fast and
fault-tolerant system that just using disk in the compute nodes.

> 
> I suspect GFS could prove useful however for enterprise clusters say 32 
> - 128 nodes where the number of IO nodes (GFS nodes with exported NFS) 
> can be small (less than 8 nodes)... it could work well

I had some experience with a NFS exported GFS system about 12
months ago and it wasn't very pleasant.  I could feel the latency
in the meta-data operations when accessing the front ends of the
cluster interactively.  It didn't surprise me because other experience
I have had with shared file-systems have been similar.

Craig

> 
> Cheers!
> Laurence
> 
> Chris Samuel wrote:
> > On Wed, 10 Nov 2004 12:08 pm, Laurence Liew wrote:
> > 
> > 
> >>You may wish to try GFS (open sourced by Red Hat after buying
> >>Sistina)... it may give better performance.
> > 
> > 
> > Anyone here using the GPL'd version of GFS on large clusters ?
> > 
> > Be really interested to hear how folks find that..
> > 
> > 
> > 
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