[Beowulf] automount on high ports

Henning Fehrmann henning.fehrmann at aei.mpg.de
Wed Jul 2 04:44:58 EDT 2008


On Wed, Jul 02, 2008 at 09:19:50AM +0100, Tim Cutts wrote:
> 
> On 2 Jul 2008, at 8:26 am, Carsten Aulbert wrote:
> 
> >OK, we have 1342 nodes which act as servers as well as clients. Every
> >node exports a single local directory and all other nodes can mount this.
> >
> >What we do now to optimize the available bandwidth and IOs is spread
> >millions of files according to a hash algorithm to all nodes (multiple
> >copies as well) and then run a few 1000 jobs opening one file from one
> >box then one file from the other box and so on. With a short autofs
> >timeout that ought to work. Typically it is possible that a single
> >process opens about 10-15 files per second, i.e. making 10-15 mounts per
> >second. With 4 parallel process per node that's 40-60 mounts/second.
> >With a timeout of 5 seconds we should roughly have 200-300 concurrent
> >mounts (on average, no idea abut the variance).
> 
> Please tell me you're not serious!  The overheads of just performing the NFS mounts are going to kill you, never mind all the network traffic going 
> all over the place.
> 
> Since you've distributed the files to the local disks of the nodes, surely the right way to perform this work is to schedule the computations so that 
> each node works on the data on its own local disk, and doesn't have to talk networked storage at all?  Or don't you know in advance which files a 
> particular job is going to need?

Yes, this is the problem. The amount of files is too big to store it
everywhere (few TByte and 50 million files). Mounting a view NFS server does not provide
the bandwidth. 
On the other hand, the coreswitch should be able to handle the flows non
blocking. We think that nfs mounts are the fastest possibility to
distribute the demanded files to the nodes. 

Henning
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