am2 MBs - 4g + SCSI wipes out root partition

[Gary Jennejohn]

On Sat, 11 Oct 2008 03:13:16 -0700
Jeremy Chadwick <koitsu at FreeBSD.org> wrote:

> On Sat, Oct 11, 2008 at 11:30:57AM +0200, Gary Jennejohn wrote:
> > On Fri, 10 Oct 2008 14:29:37 -0300
> > JoaoBR <joao at matik.com.br> wrote:
> > 
> > > I tried MBs as Asus, Abit and Gigabyte all same result
> > > 
> > > Same hardware with SATA works perfect
> > > 
> > > Same hardware with scsi up to 3.5Gigs installed works perfect
> > > 
> > > what calls my attention that all this MBs do not have the memroy hole 
> > > remapping feature so the complete 4gigs are available what normally was not 
> > > the case with amd64 Mbs for the Athlon 64 CPUs
> > > 
> > > some has an opinion if this is a freebsd issue or MB falure or scsi drv 
> > > problem?
> > > 
> > 
> > It's a driver problem.  If you want to use SCSI then you'll have to limit
> > memory to 3.5 GB.
> 
> What you're saying is that Adaptec and LSI Logic SCSI controllers behave
> badly (and can cause data loss) on amd64 systems which contain more than
> 3.5GB of RAM.  This is a very big claim.
> 
> Have you talked to Scott Long about this?
> 
> Please expand on this, and provide evidence or references.  I need to
> document this in my Wiki if it is indeed true.
> 

See the freebsd-scsi thread with Subject "data corruption with ahc driver
and 4GB of memory using a FBSD-8 64-bit installation?" from Wed, 30 Jan
2008.

This was for ahc, but the bit-rot which Scott mentions in his reply might
also apply to the LSI Logic controllers.

Basically the driver doesn't correctly handle DMA above 4GB.  Since the PCI
hole gets mapped above 4GB it causes problems.  the (S)ATA drivers don't seem
to have this problem.

---
Gary Jennejohn