ciss(4): speed degradation for Compaq Smart Array [edited]

[John-Mark Gurney]

Martin Nilsson wrote this message on Wed, Mar 30, 2005 at 22:03 +0200:
> Doug White wrote / skrev:
> >
> >I'd also suggest using a tool like iozone to run your tests instead of dd.
> >Unless your workload consists of entirely sequential writes this perf test
> >is worthless.
> 
> What is wrong with using dd to measure max read/write bandwith of the 
> controller-disk system?

It's not just measuring the bandwidth of the disk system, since it also
must read from somewhere first.. So all of your numbers read x bytes from
/dev/zero (or else where) and writes x bytes to disk, or read x bytes from
disk and writes x bytes to /dev/zero...

It is much more optimial to skip the read/write to /dev/zero, and programs
like bonnie do this...  (Though the cost of modern read/write from/to
/dev/zero, it is still measurable.)

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."