In the last episode (Jul 08), mac said:
> to keep you up to date:
> we tested with a simple dd-read on different machines and mount-points:
> 400MB file (created with "dd if=/dev/urandom of=file100Mb bs=512
> count=800000" on the intel-linux-box):
BTW - a 512-byte blocksize is basically testing how fast your kernel
can process syscalls. bs=8k or 64k would be a better test of what
mysql's activity would be.
> reading the file with dd to /dev/null on
> a) the sparc-solaris:
> local-disk: 12sec
> veritas-disk: 24sec (over fiber on symmetrix)
400/12 = 33MB/sec. Reasonable. The 24 second result (16MB/sec) on the
symmetrix is pretty low; I would have expected you to be able to max
out your fibre link (or at least hit 50% usage, which would be 50 or
100 MB/sec depending on the connection).
> b) the intel-linux
> local-disk: 2sec
200MB/sec. Very difficult to achieve on most raid-5 controllers you
can put in an Intel box. More likely is that you created the file,
then immediately re-read it, which means that you just pulled it out of
memory. You will probably need to reboot, or dismount and remount the
filesystem containing the file to ensure it reads from the disks.