[rrd-users] I/O Read overkill

Fabien Wernli wernli at in2p3.fr
Fri Oct 26 09:47:38 CEST 2007


Yesterday I migrated my dual-xeon 4GB RAID1 rrd to a quad-opteron 8GB
RAID10 server, in the hope to reduce the load.
I am managing 18k RRDs, each being updated randomly every ~10minutes
over ssh, which makes roughly 30 file updates/s.

I had many performance problems with the new server, which I was able to
manage (=server stays alive) using xfs instead of ext3, raid10 instead of
raid5. Underlying disk technology is the same (SCSI 10k drives atatched to
LSI 1030 controller), but box brand is different.

Graphs speak for themselves.
Before: 294% iowait
        4.9MB/s read (hardware raid1 hidden to linux)
        1.1MB/s write
        4.6 loadavg

After:  318% iowait
        57.9MB/s read (linux raid10 -> values have to be div by 2)
        2.3MB/s write
        8.9 loadavg

tests made with rrdtool 1.2.10 and 1.2.19.

Now where the heck do those 57.9/2 = 28.95MB/s READ come from???
I do not understand how the Read IOs were multiplied by a factor of 6!!!

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