On 2/2/2014 12:53 PM, Phillip Susi wrote:

On 02/01/2014 05:39 PM, Stan Hoeppner wrote:

quoted

It's not possible
to accurately measure IO throughput doing buffered writes.  Thus
O_DIRECT is needed.

No, you can get there just fine with buffered IO as well, unless you
have an obscenely fast array and very slow ram, the overhead of
buffering won't really matter for IO throughput ( just the extra cpu ).

Please reread my statement above.  Now let me restate that as:

Measuring disk throughput when writing through the buffer cache isn't a
measurement of disk throughput as much as it is a measurement of cache
throughput.  Thus, such measurements do not demonstrate actual disk
throughput.

Do you disagree?

-- 
Stan