Patch RFC: Promise SATA300 TX4 hardware bug workaround.

[Arno J. Klaassen]

Hello,

>  [ ... ]
> > I will test again with "#define PDC_MAXLASTSGSIZE 32*4" (just to see
> > if that makes a difference)
> >
> One thing to try is to loose any geom raid, if raid needed use ataraid
> instead.

Nope : i did a "newfs ad6" (the disk at the Promise TX4) and then an
rsync on it panics the same way as the geom_concat case did.


> I'm shuffeling boards and controllers here to try to reproduce, so far
> no luck it "just works(tm)", it seems to depend quite heavily on the
> "right" combination of possibly marginal HW....

Rather than the marginal HW part, it seems, for me, closely related to
MB/BIOS (as well (Alexander apperently has about the same setup as I
have for this test)):

a while ago (using releng_6) i tried the same setup on three different
MBs: ahd-controller + scsi-boot-disk and TX4 and three disks in
geom_mirror; results :

  - on ASUS A8? board (I use plenty of them without the sligthest
    problem for years; not really expensive but not marginal IMHO) :
    just look at it and it would crash (g_vfs_done)

  - on Tyan S28?? : rock stable, unable to crash however
    hard I tried

  - on some MSI K8 (I usually run Vista on for testing; this one I
    really bought "as cheap as possible" ) : would run OK, even 
    under rather heavy load, but when pushing really hard it 
    finaly deliveres the lovely g_vfs_done ...

I vaguely remember from another PR that the Promise card does
something with PCI-bursting which fbsd does not detect and/or
handle correctly (and beyond my simple skills as dumb tester, but
maybe the linux-sources contain a clue about that as well).

Regards and thanx for your efforts

Arno