ata controller problem

Polytropon freebsd at
Fri Oct 26 16:43:31 UTC 2012

On Fri, 26 Oct 2012 09:33:38 -0700, Jeremy Chadwick wrote:
> Regarding this:
> No no NO *NO*!

No? :-)

> I wish people would stop recommending this utter garbage.  There is
> absolutely no justification behind using the highly convoluted labelling
> mechanisms at multiple layers within FreeBSD.  There are 3 (possibly 4)
> different "label" mechanisms which do nothing but confuse the user, or
> cause other oddities/complexities.  Good grief, there is so much hard
> evidence on the mailing lists over the past 5 (maybe even 7?) years
> talking about the utter mess that is filesystem/device/geom/blahblah
> labels that to recommend this is borderline insane.

Yes, the amount of different, present (in parallel) and
differently implemented and accessible labeling mechanisms
can be confusing. There is no "the one true way" to do it.
Especially when dealing with metadata (e. g. for rare cases
of data recovery) it might make things more complicated.

I don't agree that labels in general "do nothing but confuse
the user" - the same could be said about controllers, devices
and how they are partitioned (again, many different ways here).
But users usually don't deal with that. Sysadmins do. And they
should be able to deal with it, as it's not _that_ complicated
(from their educated and experienced point of view, I assume).

That's why I would still say labels have their place, especially
in settings with many disks (10 and more) where concluding
"which disk?" is sometimes required, in terms of disk, not
disk _bay_.

> The proper way to solve this problem is to user /boot/loader.conf
> tie-downs to assign each disk to each individual controllers' device
> number (e.g. ada0 --> scbus0 --> ahcich0, or whatever you want).  Please
> note I said ahcichX, not ahciX.  Different things.
> I have helped others in the past do this; Randy Bush is one such person.
> Taken directly from my /boot/loader.conf with a single SATA controller,
> but obviously this can be adjusted to whatever you want.
> # "Wire down" device names (ada[0-5]) to each individual port
> # on the SATA/AHCI controller.  This ensures that if we reboot
> # with a disk missing, the device names stay the same, and stay
> # attached to the same SATA/AHCI controller.
> #
> #

That's a very nice contribution to the topic - I hadn't thought
it was that easy, and it actually solves the "who comes first"
kind of problems.

> See CAM(4) man page (read it, don't skim!) for full details.  Just
> please for the love of god do not use labels to solve this.

Thanks, this contains inspiration of maybe how to make access to
USB devices and memory card readers more efficient (i. e. making
sure they are always represented by one and the same device, instead
of "the next free one").

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

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