On Wed, Dec 31, 2008 at 9:42 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. > > The above tests are pretty consistent. /dev/sde is a raid5 array, > hardware raid. > > So my question here is, wtf? I've been working to do a backup which I > would think would either cause network utilization to max out, or disk io > to max out. I'm not seeing either. Sar says the disks are 100% utilized > but I can cause major increases in actual disk reads and writes by just > running additional commands. Also, if the disks were 100% utilized I'd > expect we would see lots more iowait. We're not though, iowait on the box > is only %0.06 today. > > So, long story short, we're seeing much better performance when just > reading or writing lots of data (though dd is many times slower then cat). > But with our real-world traffic, we're just seeing crappy crappy IO. > > Thoughts, theories or opinions? Some of the sysadmin noc guys have access > to run diagnostic commands, if you want more info about a setting, let me > know. > > I should also mention there's lots going on with this box, for example its > hardware raid, lvm and I've got xen running on it (though the tests above > were not in a xen guest). > Could you perform an hdparm -tT on that disk ? Also, output an strace against your cat & dd commands. if my memory is good enough, cat use mmap() which is faster than read() (which is used by dd) -- Xavier.t Lamien -- _______________________________________________ Fedora-infrastructure-list mailing list Fedora-infrastructure-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/fedora-infrastructure-list
