[rrd-users] I/O Read overkill
wernli at in2p3.fr
Sun Oct 28 11:00:10 CET 2007
On Fri, Oct 26, 2007 at 05:53:33AM -0700, Jason Fesler wrote:
> I wonder if it is the defaults for readahead. "man blockdev" and search
> for readahead. You might read what your defaults were on the old kernel;
> and temporarilly apply them to your drives under the new kernel, and see
> what happens with 1.2.10.
yeah I was planning on doing that, however now my production system is
up and running again so... ;)
Here are the values before (RRDs on sda):
# /sbin/blockdev --getra /dev/sda
and after (RRDs on md10 raid1+0):
# /sbin/blockdev --getra /dev/sd[b-e] /dev/md /dev/md10
(siectorsiwe is 512 in both cases)
So I went from 120 to 512. Does that mean 4.266 times more data was being read
off the drive? This doesn't account for the difference though, as I went
from average read of 730KB/s to 36.2MB/s (sorry my previous values were
wrong I mistook Avg for Max), which is a factor of more than 50(!). So
unless the response is non-linear, I guess I have to look elsewhere...
I still suspect a 64bit issue, what do you think?
Now that I use rrdtool 1.2.99999[...] the read value dropped even further:
84KB/s, which is consistent with the announcement by the author (10x more
updates per second).
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