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> Have a look at this paper: http://people.redhat.com/nhorman/papers/rhel3_vm.pdf > It's RHEL3 specific but it will give you an idea about what you need to tune. > > Is it really a problem that the file cache is taking all the unused > memory? As long as the pages are "clean" the kernel can throw them out > easilly without any problems. You might want to tune vm.bdflush though > to be more aggresive so dirty pages are written to disk as fast as > possible. Thanks for the information. We may also end up upgrading to the 2.6 kernel. Cheers, Greig > With n multiple streams dcache writes data like: > stream: write 10K, seek ahead (n-1)*10K, write 10K, .... > ....... > With 1 stream you get: > stream: write 10K, write 10K, ... > > If the data from all the streams doesn't arrive at the same time > you end up with writes all over the place and your disk IO suffers > as a result. The 3ware raid cards that we use at IC get around > ~70MB/sec at sequencial IO and around ~1-5MB/sec at random IO in > RAID5. It's only a guess in my part that the parallel streams cause > that much random IO or not since i didn't had that much time to test > different settings during the FTS transfers :( > > Cheers, > Kostas > -- ======================================================================= Dr Greig A Cowan http://www.ph.ed.ac.uk/~gcowan1 School of Physics, University of Edinburgh, James Clerk Maxwell Building DCACHE PAGES: http://www.gridpp.ac.uk/deployment/admin/dcache/index.html =======================================================================