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Message-ID: <CAA3ZYrCgMmGi3EHKEuXb=qWPjC2zSMYcfgZ6nh-ipqQ7dAeVdA@mail.gmail.com>
Subject: Re: IBM blade server abysmal disk write performances
From: Dieter BSD <dieterbsd@gmail.com>
To: freebsd-hackers@freebsd.org
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Cc: gibbs@FreeBSD.org, scottl@FreeBSD.org, mjacob@FreeBSD.org
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> I am thinking that something fancy in that SAS drive is
> not being handled correctly by the FreeBSD driver.

I think so too, and I think the something fancy is "tagged command queuing".
The driver prints "da0: Command Queueing enabled" and yet your SAS drive
is only getting 1 write per rev, and queuing should get you more than that.
Your SATA drive is getting the expected performance, which means that NCQ
must be working.

> Please let me know if there is anything you would like me to run on the
> BSD 9.1 system to help diagnose this issue?

Looking at the mpt driver, a verbose boot may give more info.
Looks like you can set a "debug" device hint, but I don't
see any documentation on what to set it to.

I think it is time to ask the driver wizards why TCQ isn't working,
so I'm cc-ing the authors listed on the mpt man page.