Re: NFS synchronization problems on Beowulf cluster

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Mon, 2006-07-17 at 15:17 -0300, Mario Storti wrote:
> Hi all, 
> 
> We have still problems with NFS in our Beowulf cluster. The original
> post is here
> 
> http://thread.gmane.org/gmane.linux.nfs/9564/focus=9566
> 
> The news are that we reproduced the problem on Scientific Linux 4.2
> and also without VNFS. In addition we have taken a tethereal capture
> that may help in understanding the problem. 
> 
> In brief we have a Beowulf class cluster built on Scientific Linux
> (Beryllium) 4.2, (kernel 2.6.9-22.0.1). The cluster is disk-less
> (nodes don't have hard disks) based on the Warewulf package. NFS
> traffic is reduced by using VNFS filesystems at the nodes. However we
> reproduced the problem in a configuration with disks at the nodes. 
> 
> The problem is that for some files in user accounts if we make some
> modifications to the file in the server, this changes are not seen in
> the compute nodes. The NFS server is NFS3 and with the standard
> configuration (8 instances of the server and default parameters). The
> cluster has 20 nodes at this time, but we have made experiments with a
> `cloned' cluster and even with only two nodes the problem persist.
> 
> The experiment is as follows: We change a text file in a user account
> with Emacs and checking whether the change is seen in the compute
> nodes. Sometimes the change is immediately seen in the compute nodes,
> but many times some nodes don't see the change. 
> 

This is a FAQ that has been well-publicised and discussed to death on
this list:
  http://nfs.sourceforge.net/#faq_a8

Trond


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