Fwd: Re: Please help. Can't see HD

[Sergey 'DoubleF' Zaharchenko]

On Mon, 29 Dec 2003 14:57:13 +1030
Malcolm Kay <malcolm.kay at internode.on.net> probably wrote:

> On Mon, 29 Dec 2003 14:39, Francisco Reyes wrote:
> > On Mon, 29 Dec 2003 14:27:01 +1030, Malcolm Kay wrote:
> > >This is likely your problem source!!!
> > >
> > >/dev/rad[n] is an alias of /dev/ad[n]; that is it refers to IDE drive n.
> > >(Historically they had somewhat different meanings but even then still
> > >refered to the same physical device -- the 'r' means raw)
> > >
> > >If n was 2 you have over written the beginning of ad2.
> >
> > Well I guess the good news is that the HD is probably ok then.
> >
> > :-)
> 
> Yes; should be.
> >
> > In FAT I seem to recall there are two copies of the boot sector.
> > Does FreeBSD has anything like that?
> >
> 
> I seem to recall some options or utilities under MS-DOS that did 
> something like that, but think this was mainly for floppies.
> Certainly there are duplicate copies of the FAT allocation tables,
> but these are next to one another on the disk so don't really protect
> against this sort of calamity.
> 
> I guess the nearest thing in FreeBSD is mutiple copies of the 
> superblocks within the file system, but unless you can reconstruct 
> the slice table(partition in MS terms) I don't believe it will help.
> 
> > If what I did trashed the first sectors would that have affected
> > all mount points?
> 
> How big was the image you copied to the disk? -- that should tell
> you how much of your drive is overwritten.
> 
> It is probable your disklabel has also disappeared, so you 

And the superblock, and some large piece of data.

> probably need to reconstruct both the slice table in the MBR and 
> the disklabel in the first slice. With some vague recollections of 
> what you did originally to install FBSD it is possible that some 
> lucky guesses might work.

For the `slice table' (MBR) sysutils/gpart could be of some help. Not
sure about the disklabel, though. 

> If you can find the first sector of a slice carrying an installed file

Where `find' might mean 

# hd < /dev/ad6s1 | grep "54 19 01 00"

if looking for a ufs1 filesystem or

# hd < /dev/ad6s1 | grep "19 01 54 19"

for ufs2. (see the archive for details; in the discussion the method
seemed to work)

> system then this might hold a copy of the slice table allowing
> reconstruction of the original MBR with some confidence. 
> 
> Malcolm Kay
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-- 
DoubleF
Vote for ME -- I'm well-tapered, half-cocked, ill-conceived and
TAX-DEFERRED!

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