AHCI/ATA_CAM for dummies?

b. f. bf1783 at googlemail.com
Tue Dec 15 03:35:44 UTC 2009

On 12/14/09, Adam Vande More <amvandemore at gmail.com> wrote:
> On Mon, Dec 14, 2009 at 2:47 PM, Doug Barton <dougb at freebsd.org> wrote:
>> b. f. wrote:
>> > On 12/14/09, Doug Barton <dougb at freebsd.org> wrote:

>> I did look up the spec sheet on the hard drive last night, and
>> although it does mention SATA and NCQ it does not explicitly mention
>> AHCI.

This isn't surprising, because, as mentioned before, AHCI is largely
concerned with the workings of host controllers, and not with most
storage devices.  It is reassuring to see that the specs agree with
our drivers with respect to the NCQ.

> A bit of research leads to believe you are SOL on ahci/NCQ for this system
> unless you're able to hack a BIOS.  I believe both drive and controller are
> capable of running it, but Dell has disabled it as an option for some
> reason.

As Adam says, a brief look at the web shows that people have long been
complaining about the fact that the BIOS of these machines does not
allow users to employ AHCI.  If, as you say, Dell hasn't been willing
to fix this, then you are left with only a few options:

1) try to find a replacement BIOS ( maybe someone is working on
coreboot support for this model? :
http://www.coreboot.org/Welcome_to_coreboot )

2) employ a driver that circumvents the crippled BIOS, and enables AHCI.

With regard to 2), there have been a number of hacks for Linux that
enable AHCI on these and related machines, with varying degrees of
success. See, for example:

(and follow-ups!)

Maybe a knowledgeable person, like mav@ or jhb@, could exploit some of
these ideas in FreeBSD to allow you and others in similar predicaments
to use AHCI on your machines?


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