a new hard-drive in a 2y/o laptop

Chris Brennan xaero at xaerolimit.net
Sun Jan 2 06:15:57 UTC 2011

On Sat, Jan 1, 2011 at 10:20 PM, Ian Smith <smithi at nimnet.asn.au> wrote:

> Well, what's commonly called 'the partition table' is bytes 0x1be-1ff of
> the MBR, so I was confused by your writing to sector 1 rather than 0,
> but have a new theory to test, seeing Chris isn't making any progress;
> this maybe a victim of the old 'slice vs partition' terminology issue.
I think I was able to figure this part out, his meaning at least.

>  The bsdlabel lives in sector 1 (counting from 0) of the slice concerned,
> specifically the first 0x114 (276d) bytes, in the second sector of the
> boot blocks.  As noted above, in unsliced disks such as memstick.img
> that's sector 1 of the entire disk, but in ordinary sliced disks it's in
> sector 1 of the _slice_, so if you'd used (here using Chris' ad4)
>  dd if=/dev/zero of=/dev/ad4s1 oseek=1 bs=512 count=1
I would happily run this, but ad4s1 doesn't exist, and hasn't (that I know
of), I did do oseek=0 and oseek=1 on /dev/ad4 tho and that didn't change
anything, it still says it can't find /dev/ad4s1b (swap obviously)

> - rather than of=/dev/ad4 - then you would indeed be zeroing out the
> label, ie the 'partition table' in FreeBSD-speak.  Is that perhaps what
> you had to do to that 6.2 disk, which I suppose was a sliced disk?
> At 6.x (and 7.x, I think) it could have been 'dangerously dedicated' ie
> unsliced .. which option has been removed in 8.x _except_ regarding the
> memstick.img (appearing as /dev/daXa) .. not half confusing, eh?
I actually noticed this today, I had issues writing 8.2BETA1 to a 2GB
MicroSD card, so I used a 2.5" external hard-drive and from the fixit prompt
I noticed that it wrote a 1gb partition for the BETA1 image and left the
rest of the desk untouched (ann 59gb of it).

> In any case, it'd be a cheap trick for Chris to try from Fixit, and
> though it seems unlikely there'd be anything 'leftover' from an earlier
> install, maybe earlier failure/s have left a broken bsdlabel there?
> So at this still-uninstalled stage it couldn't hurt to zero that sector,
> or even the first 4KB of ad4s1 .. which is /boot/boot1 plus /boot/boot2
> (which equals /boot/boot !) before the label section gets written.  ie:
>  sysctl kern.geom.debugflags=16
>  dd if=/dev/zero of=/dev/ad4s1 bs=512 count=8
> will remove slice 1's boot blocks entirely, including the bsdlabel.
> cheers, Ian
> [excuse broken threading, but unless cc'd I have to reply to the digest]

I've been trying to keep you in my replies but your down-under, so I don't
get your replies till after 1am my time... Anywho, it's late and I need to
be up in 8hrs, hopefully this can be figured out ... I would hate for the
disk to be defective in some way.

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