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On 02/04/2014 04:58 PM, Stan Hoeppner wrote:

Yes, I stated that in this post

http://www.spinics.net/lists/raid/msg45726.html

in the context of achieving greater throughput with an FIO job
file configured to use O_DIRECT, a job file I created, that the OP
was using for testing.  That job file is quoted further down in
this same post, and is included in my posts prior this one in the
thread.  Apparently you ignored them.  The context of my comment
above is clearly established multiple times earlier in the thread.

In my paragraph directly preceding the statement you quote above,
I stated this:

"Serial submission typically doesn't reach peak throughput...  You 
usually must submit asynchronously or in parallel to reach maximum 
throughput."

And again this is in the context of the FIO job file using
O_DIRECT, and this statement is factual.  As I repeated earlier
today, O_DIRECT is used because measuring actual throughput at the
disks is straightforward.  To increase O_DIRECT write throughput in
FIO, you typically need parallel submission or AIO.  This is well
known.

Ahh, I did not gather that O_DIRECT was already assumed.  In that
case, then I was simply restating the same thing: that you want aio
with O_DIRECT, but otherwise, buffered IO works fine too ( which is
what the OP was using with dd, which is why it sounded like you were
saying not to do that, that you must use O_DIRECT + aio because
buffered IO won't get you the performance you're looking for ).


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