Re: Why are disk writes so slow?

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As in his example (with a bufsize of 8192),

time ./a.out < 1.5M-testfile > /dev/null

runs five times faster than (clock time)

time ./a.out < 1.5M-testfile > /a.out.out

a) your 1.5M-testfile is most likely still in the cache from previous test runs or from when you created it.

b) reading and writing to the same disk, you're going to thrash the disk with seeks.

so, some other experiments to try might include:

a) create a whole bunch of test files, reboot, and then make sure you use a different test file for every run.

b) try variations where you use a ramdisk for the read and disk for the write, then a disk for the read and a ramdisk for the write, and then a ramdsik for both.

c) try reading from /dev/zero and writing to disk as the converse of reading from disk and writing to /dev/null, etc.


-Jason
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