Can FreeBSD safely use a (un-booted from) drive that is invisible to the BIOS?

Kevin Kinsey kdk at
Sat Apr 1 15:47:13 UTC 2006

Danny MacMillan wrote:

>I have a machine with the following two drives (as listed in dmesg):
>ad0: 12427MB <Maxtor 91303D6 GAS54A12> at ata0-master UDMA33
>ad2: 76319MB <Maxtor 6L080P0 BAJ41G10> at ata1-master UDMA33
>ad0 is the boot drive.  It is recognized by the BIOS, obviously, and
>has been in the machine for some years.  ad2 is a new drive I just
>added to the machine yesterday.  It is not visible to the BIOS at all.
>If anyone can posit a reason it would not be visible to the BIOS, I
>would like to know the answer.  The BIOS supports LBA and ad0 is more
>than 8GB so it wouldn't appear to be the 8GB limit, and the next limit
>I am aware of is comfortably larger than 76GB.

There were quite a few BIOSes that had a 32GB limit; thus,
HD manufacturers contrived a (usually) dual-jumpered configuration
to limit the reported disk size to 32 GB for these boards.  In
my experience (which is not extensive) these would be relatively
early ATX boards (Pentium II, early K6/2's, etc.).

Kevin Kinsey

Sentient plasmoids are a gas.

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