From mboxrd@z Thu Jan  1 00:00:00 1970
From: Greg <itooo-xVucS5mfmt0AvxtiuMwx3w@public.gmane.org>
Subject: Re: RBD vs RADOS benchmark performance
Date: Mon, 13 May 2013 17:10:37 +0200
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To: Gandalf Corvotempesta <gandalf.corvotempesta-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
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Le 13/05/2013 17:01, Gandalf Corvotempesta a =E9crit :
> 2013/5/13 Greg <itooo-xVucS5mfmt0AvxtiuMwx3w@public.gmane.org>:
>> thanks a lot for pointing this out, it indeed makes a *huge* difference !
>>> # dd if=3D/mnt/t/1 of=3D/dev/zero bs=3D4M count=3D100
>>>
>>> 100+0 records in
>>> 100+0 records out
>>> 419430400 bytes (419 MB) copied, 5.12768 s, 81.8 MB/s
>> (caches dropped before each test of course)
> What if you set 1024 or greater value ?
> Is bandwidth relative to the read ahead size?
Setting the value too high degrades performance, especially random IO =

performance.
You have to determine  the right choice for your usage.

Cheers,