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Date:      Wed, 12 Dec 2012 14:42:43 +0100
From:      Stefan Esser <se@freebsd.org>
Cc:        freebsd-hackers@freebsd.org
Subject:   Re: FreeBSD for serious performance?
Message-ID:  <50C889D3.1050404@freebsd.org>
In-Reply-To: <CAJ-Vmok-DtKwNW2DJ21E_UBcf%2B3CWHJ0Z8FyiNC=mycKUFNuBA@mail.gmail.com>
References:  <20121211204323.310760@gmx.com> <CAJ-Vmok-DtKwNW2DJ21E_UBcf%2B3CWHJ0Z8FyiNC=mycKUFNuBA@mail.gmail.com>

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Am 11.12.2012 22:40, schrieb Adrian Chadd:
> .... I'm not seeing:
> 
> * any references to driver code that exhibits that very broken behaviour;
> * any patches from you to implement NCQ on your nforce chipset;
> * any offer of incentive to any developer to add that support.
> 
> Now, (1) is definitely worrying but as you've not provided any actual
> information, the level of helpfulness of this comment is 0.
> (2) and (3) would go a long way to making FreeBSD "better".

Yes, but the answer to (1) seems to be very simple:

The cause of the low write performance is the disabled write cache.
Enabling the write cache is unsafe on SATA drives (with or without
NCQ), since they do not make any guarantees that nearby data is not
lost if power fails during a disk write. It never happened to me,
but there is a reason that SAS drives have less capacity, much lower
BER (one to two magnitudes) and are more expensive than SATA drives.

The solution to the performance problem is simple: Turn on the write
cache. If the data is valuable, then SAS is the solution to both the
performance and the inherent reliability problems. If SATA with NCQ
really provides acceptable reliability, then a cheap SATA controller
with NCQ support in FreeBSD might also be an option, at a cost that
would pay one developer hour. Asking Nvidia to release the confidential
documentation for their chip-set might help, but I doubt that there is
much interest to add support for NCQ to an obsolete chip-set, today,
unless you pay a developer (and even then ...).

If all these don't work for you, then you may really be better served
by Linux with the drivers donated by Nvidia.

And if you buy a new system, you may consider choosing components
from vendors that do not provide binary blobs for selected operating
systems, but publish the necessary documentation for driver writers
(or which develop open source drivers for FreeBSD, not only for Linux).

There are so many ways to solve your problem



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