On Jul 7, 2007, at 06:14, Orvar Korvar wrote:
When I copy that file from ZFS to /dev/null I get this output:
real 0m0.025s
user 0m0.002s
sys 0m0.007s
which can't be correct. Is it wrong of me to use "time cp fil fil2"
when measuring disk performance?
well you're reading and writing to the same disk so that's going to
affect performance, particularly as you're seeking to different areas
of the disk both for the files and for the uberblock updates .. in
the above case it looks like the file is already cached (buffer cache
being what is probably consuming most of your memory here) - so
you're just looking at a memory to memory transfer here .. if you
want to see a simple write performance test many people use dd like so:
# timex dd if=/dev/zero of=file bs=128k count=8192
which will give you a measure of an efficient 1GB file write of
zeros .. or use a better opensource tool like iozone to get a better
fix on single thread vs multi-thread, read/write mix, and block size
differences for your given filesystem and storage layout
jonathan
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