On 03/09/2012 08:42, Przemek Klosowski wrote:
On 03/09/2012 01:43 AM, Adam Williamson wrote:
On Thu, 2012-03-08 at 22:19 -0700, Chris Murphy wrote:
I'm not sure how useful 'time' is as a benchmark for file copies.
Don't file transfers get cached and return to a console as
'complete'
long before the data is ever written, sometimes?
I'm pretty sure you sometimes hit the case where you copy 200MB to a
USB
stick, it returns to the console pretty fast, but the light on the
stick
is still flashing, and if you run 'sync', it sits there for quite a
while before returning to the console, indicating the transfer
wasn't
really complete. So I'm not sure 'time'ing a 'cp' is an accurate
test of
actual final-write-to-device.
That is true---but in that case, we could flush the disks. and then
time the operation followed by another flush, i.e.:
sync; time (cp ...; sync)
I assume that the old-time Unix superstition of calling sync three
times no longer applies :)
Perhaps a dedicated disk benchmark like bonnie++ would be a better
test, though.
If you want to look seriously into file-system benchmarking I would
suggest looking into the work done by the fsbench people at Stony Brook
University's Filesystem and Storage Lab (FSL). There is a survey paper
there for the last decade of FS benchmarks and their short commings and
what should be addressed.
http://www.fsl.cs.sunysb.edu/project-fsbench.html
Dave
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