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To: freebsd-hackers@freebsd.org,
 Karim Fodil-Lemelin <fodillemlinkarim@gmail.com>
Subject: Re: IBM blade server abysmal disk write performances
References: <CAA3ZYrB+4LU=YRQsvYB19sE9ywjejyP7Gc4j8fpTGx2LaZm4kw@mail.gmail.com>
 <50F87741.4030201@gmail.com>
Date: Fri, 18 Jan 2013 09:16:50 -0600
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From: Mark Felder <feld@feld.me>
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On Thu, 17 Jan 2013 16:12:17 -0600, Karim Fodil-Lemelin  
<fodillemlinkarim@gmail.com> wrote:

> "SAS controllers may connect to SATA devices, either directly connected  
> using native SATA protocol or through SAS expanders using SATA Tunneled  
> Protocol (STP)."
>  The systems is currently put in place using SATA instead of SAS  
> although its using the same interface and backplane connectors and the  
> drives (SATA) show as da0 in BSD _but_ with the SATA drive we get *much*  
> better performances. I am thinking that something fancy in that SAS  
> drive is not being handled correctly by the FreeBSD driver. I am  
> planning to revisit the SAS drive issue at a later point (sometimes next  
> week).

Your SATA drives are connected directly not with an interposer such as the  
LSISS9252, correct? If so, this might be the cause of your problems.  
Mixing SAS and SATA drives is known to cause serious performance issues  
for almost every JBOD/controller/expander/what-have-you. Change your  
configuration so there is only one protocol being spoken on the bus (SAS)  
by putting your SATA drives behind interposers which translate SAS to SATA  
just before the disk. This will solve many problems.