On Wed, Dec 31, 2008 at 1:42 PM, Mike McGrath <mmcgrath@xxxxxxxxxx> wrote: > Lets pool some knowledge together because at this point, I'm missing > something. > > I've been doing all measurements with sar as bonnie, etc, causes builds to > timeout. > > Problem: We're seeing slower then normal disk IO. At least I think we > are. This is a PERC5/E and MD1000 array. > > When I try to do a normal copy "cp -adv /mnt/koji/packages /tmp/" I get > around 4-6MBytes/s > > When I do a cp of a large file "cp /mnt/koji/out /tmp/" I get > 30-40MBytes/s. > > Then I "dd if=/dev/sde of=/dev/null" I get around 60-70 MBytes/s read. > > If I "cat /dev/sde > /dev/null" I get between 225-300MBytes/s read. I thought the /dev/null numbers were not good indicators (I remember Stephen Tweedie or someone in the RH Kernel team lecturing that numbers while consistent would not show real world issues and could be much higher than what really happens.) The lesson was always send it to a real file that its going to open/close/deal with.. even if the file is in a ram disk. I do know that dd defaults to 512 block size which makes it different speeds for copies (whoops Ricky confirms this ). Also stuff that will fit inside of the PERC Cache and how the journal is going to be written/committed are going to make differences... The next difference is how a system sees inside of a disk and how the disk sees itself. The /dev/xxx are always going to be much higher because there is no filesystem interaction and the controller is going to be just pulling from hardware.. it might even optimize doing that (raw partition style) so that you get insane speeds but as soon as you put in a filesystem poof. -- Stephen J Smoogen. -- BSD/GNU/Linux How far that little candle throws his beams! So shines a good deed in a naughty world. = Shakespeare. "The Merchant of Venice" _______________________________________________ Fedora-infrastructure-list mailing list Fedora-infrastructure-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/fedora-infrastructure-list
