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All our SM 'twins' are 8-core beasties (2 x 4-cores) per side. They all sit on a 1GbE network (Nortel 5510/5530 etc). To answer you question - yes there will be contention if one or more jobs want to do i/o to the net at the same time. This happens whatever the speed of the NIC. If you have a 100Mb/s NIC, then in general, everything will take ~10 times as long than for a 1Gb/s NIC for a single process. If you have two processes, the transaction(s) will take >10 times as long because of context switching between processes for the resource (the NIC). If your jobs are running several tens of hours, then a 100 second data squirt at the end is insignificant compared to the run time - and making it 200 seconds is still insignificant. However for high-i/o jobs where the i/o is 'continuous' then it could double your run time. It may be that your data sink is the limiting factor - if it is a 1GbE system, then you could get 10 x 100Mb/s data streams off it (assuming that it can get the data on/of the disk that fast). The best strategy is to force the jobs to do their I/O to the local disk and and then squirt it off in one lump at the end of the job. The input data has to be pre-staged locally too. Then the normal smearing out of start and finish of jobs due to slightly different run times spreads the high load to the servers as well. Martin. -- Martin Bly RAL Tier1 Fabric Team > -----Original Message----- > From: Testbed Support for GridPP member institutes > [mailto:[log in to unmask]] On Behalf Of Winnie Lacesso > Sent: 29 August 2008 13:59 > To: [log in to unmask] > Subject: 8-core WN with single NIC - contention? > > Question for those of you with 8-core WN, where something like > gpfs is *not* in the equation - do you have these on a 1Gbps > network or a 100Mbps network? > > Because one wonders, if WN are on a 100Mbps network could there be > contention between several high-I/O jobs on that WN for that single > 100Mbps eth0 NIC? > > Anyone seen this? >