On Wed, Jul 4, 2012 at 8:16 PM, Carsten Mattner <carstenmatt...@gmail.com> wrote: > On Wed, Jul 4, 2012 at 8:11 PM, Carsten Mattner > <carstenmatt...@gmail.com> wrote: >> On Wed, Jul 4, 2012 at 8:07 PM, Matthew Dillon >> <dil...@apollo.backplane.com> wrote: >>> >>> :Thanks Matt for the explanation and tip. >>> : >>> :It did of course hang when I tried to DEL into the BIOS. >>> :What worked is pulling out the sata connector, entering >>> :the BIOS putting it back and then detecting the disk. >>> :Interesting the auto detection then worked. I've explicitly >>> :set it to LARGE and now I can boot a rescue cd. >>> : >>> :How many bytes should I zero out for the disk to be >>> :"normal" again? 512bytes? 4megs? >>> >>> The BIOS is basically just accessing the slice table in the first >>> 512 bytes of the disk. If I want to completely wipe a non-GPT >>> formatted disk I usually zero-out (with dd) the first ~32MB or so >>> to catch both the slice table and the stage-2 boot and the disklabel >>> and the likely filesystem header. >>> >>> Destroying a GPT disk requires (to be safe) zero'ing out both the first >>> AND the last X bytes of the physical media to also ensure that the >>> backup GPT table is also scrapped. Again, to be safe I zero-out around >>> 32MB at the beginning and 32MB at the end w/dd (if it's GPT). >> >> How do I tell dd to delete x bytes at the end of device? Negative values? > > Will try seek=nG
dd's seek= operates on blocks so have to supply multiple of bs=. Thanks again Matt and everybody.
