Re: Very long raid5 init/rebuild times

[Phillip Susi <psusi@ubuntu.com>]

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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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