Phoenix BIOS, hard disk data loss

[Dan Strick]

On Thu, 4 Dec 2003, xscd at xscd.com wrote:
>>
> Some months ago, just after buying a Tyan Tiger s2466 MPX dual processor
> motherboard and installing FreeBSD 5.0 on it, I experienced a lot of
> data loss (lost files and directories, unrecoverable by fsck). I
> thought the problem might be related to disk geometry (I'm fairly new
> to FreeBSD and the sysinstall disk geometry warning concerned me).
>
> However, after a couple months I decided to change just one setting in
> the Phoenix BIOS: Large Disk Access Mode
>
> There are two options for Large Disk Access Mode: "DOS" and "Other"
>
> The help text for this item says: "This option denotes that a hard drive
> with more than 1024 cylinders, more than 16 heads and or more than 64
> tracks per sector is present. Choose OTHER when using OSes such as
> UNIX."
>
> So, at first I had chosen "Other." However, after all the data loss, I
> felt I had nothing (more) to lose so I changed it to DOS just to see if
> it made a difference. Apparently it did. I have experienced no more
> lost data (from hard disk corruption or problems) in the six or so
> months since I made the change.
>>

The large disk option sounds like it affects the "translated" disk
geometry used by BIOS to increase the amount of disk accessible to
software that uses the BIOS for disk i/o (e.g. DOS).  FreeBSD uses
the BIOS disk i/o facilities only to read the disk when booting.

It is highly unlikely that your file system corruption problems were
related to the BIOS Large Disk Access Mode option unless you were also
using a non-FreeBSD OS on the same disk and it inadvertently did disk
writes through the BIOS to wrong disk locations.

Dan Strick
strick at covad.net