In message <[EMAIL PROTECTED]> Andrew Hesford writes:
: On Sat, Apr 07, 2001 at 07:26:30PM -0600, Warner Losh wrote:
: > In message <[EMAIL PROTECTED]> Andrew Hesford writes:
: > : Hrm... I'm sorry then. I have no idea why the Handbook asks you to zero
: > : out the device, it consumes a lot of time and really isn't necessary. I
: > : wonder if that could be the source of your problem.
: >
: > The handbook should say that only the first cylendar (usually 1M)
: > should be zeroed.
:
: Why is it important to zero out the first cylinder? I can understand
: wiping the first sector to destroy the MBR (although I don't see why
: this matters, either), but what makes the first cylinder special?
Because our bootblock insertion code can be stupid. There are many
cases when you fdisk -I and then disklabel a disk where the MBR will
be hozed (I think this is only the copy of the MBR in the boot1 image
located in the second track of the disk). We have found that this
second copy of the MBR, which is almost always bogus, confuses
things. dd of /dev/zero for the first track or so cures this and
allows us to lay down correct MBR and freebsd disk label.
A cylinder might be overkill, but it is what we do on the CF that we
make bootable.
Warner
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