How to slow down SATA to 1.5 GBit/s ?

[Juergen Lock]

In article <106107651416886 at 192.168.2.69> you write:
>Hi,
Hi!
>
>Juergen Lock gave me a lot to read about
>> ahci(4) on FreeBSD >= 8.0
>
>The proposed solution points me to a third way
>how a contemporary burner can be driven by
>FreeBSD.
>
>The purpose of my FreeBSD installation is to
>improve libburn on FreeBSD and to provide
>support for FreeBSD users. I.e. i want to run
>a contemporary production system with all
>possible variations of drive attachment.
>My idea was to use the same burner via USB and
>via eSATA alternatively.
>
>So even if i get ahci running i would still
>need a solution for ata.
>(If there is none, then i will have to put
> the drive into the computer and use SATA
> without "e". No easy switch to USB then.)
>
 Ah ok, I see...  And thanks for trying to help improving libburn! :)

 Btw there also is siis(4) which works pretty much the same as ahci(4),
only its for SiliconImage sata controllers.  (And then you can also
connect sata drives on sas controllers although I'm not sure if anyone
tested burning there yet...  I do know of someone who was able to boot
and install FreeBSD from an optical drive connected that way tho.)

 And if you are also testing bluray you might need another patch:
	http://www.freebsd.org/cgi/query-pr.cgi?pr=138789
(Actually the patch also was needed for an external optical drive
connected on usb to read `pressed' dvds for one guy, but since you
use a `normal' sata drive with an usb interface your drive probably
isn't affected - unless it is bluray.)

>------------------------------------------------
>
>I will nevertheless try to get my fstab ready
>for ahci and to learn how to boot with that.
>After all, it seems to be the upcomming driver
>for SATA.
>
>Not being a skilled sysadmin i wonder whether
>this hint by Juergen announces trouble:
>
>> (you still have to take care of swap manually then tho, and dumpdev in
>> rc.conf if you have it set explicitly.)
>
>The machine is generously equipped with RAM.
>Vanilla installation from 8.0-RELEASE-amd64-dvd1.iso.gz
>plus some ports around CD/DVD/BD burning.
>Installation was easy. :)
>
>Can it be that it doesn't have any swap ?
>
>  # swapinfo
>  Device          1K-blocks     Used    Avail Capacity
>  # vmstat
>   procs      memory      page                    disks     faults         cpu
>   r b w     avm    fre   flt  re  pi  po    fr  sr ad4 cd0   in   sy   cs us sy id
>   0 0 0    435M  3711M    64   0   0   0    56   0   0   0    2   94  448  0  0 100
>
>Nothing gets found by
>  # fgrep dump /etc/rc.conf
>Is that a good sign ?
>
 Well if you didn't create a swap partition during install then you
don't have one. :)  A swap partition has another use besides, well,
swapping if you are low on ram:  Taking a crashdump in case of a kernel
panic etc. (that is what dumpdev configures), in order to get a full
kernel backtrace or otherwise look at the saved state of a panic'd
kernel, i.e. it is to help debugging...  But btw there has been code
added recently to allow dumping onto an usb key/disk too so if all else
fails and your FreeBSD is new enough you might still be able to get a
backtrace that way.  I don't remember if that code is in 8.0 already so
you might need stable/8 or head tho; it is not in 6.x or 7.x because it
needs the new usb stack.

 Anyway, good luck!
	Juergen