> Glen Dosey <[EMAIL PROTECTED]> wrote > On Fri, 2007-08-24 at 08:45 -0400, Lawrence Sorrillo wrote: > > I am uncertain what this step does.... > > > > now we unmount the NFS share, recreate the file on the server, and remount > > it to clear the client cache but leave it cached on the server > > > > [EMAIL PROTECTED] ~]# dd if=/mnt/array3/file.dd of=/dev/null bs=4k > > 524287+0 records in > > 524287+0 records out > > 2147479552 bytes (2.1 GB) copied, 18.5161 seconds, 116 MB/s > > > > > > What does it accomplish? > > I was using this step to illustrate that NFS itself is capable of > transferring data across the GigE network at near wires speeds. > > By unmounting the NFS share we clear the file from being cached in RAM > on the client, ensuring that it must be gotten from the server again via > NFS as opposed to being grabbed from RAM on the client.
I ran into a nasty bug involving "dump" on recent kernels, the long and still not fully resolved story is here: http://bugzilla.kernel.org/show_bug.cgi?id=8636 In a nutshell, dump on recent kernels runs hideously slow on (P)ATA disks (by a factor of 6!) because of this change in the .config file: -CONFIG_DEFAULT_IOSCHED="cfq" +CONFIG_DEFAULT_IOSCHED="anticipatory" (cfq in the new kernels, anticipatory in the old ones). The "fix" was: echo "anticipatory" > /sys/block/hda/queue/scheduler Now this may be completely irrelevant, for instance, there was no problem with the SCSI disks I tested, but there might be with your raid controller. If NFS can move the data across the network at full speed, but can't seem to read nearly as fast as the controller, it's possible that the scheduler you're using is involved. There are 4 to choose from, perhaps give them all a test and see if any of them improve matters? Regards, David Mathog [EMAIL PROTECTED] Manager, Sequence Analysis Facility, Biology Division, Caltech _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
