documentation of GEOM data structures needed

[symbolics at gmx.com]

On Mon, Nov 11, 2013 at 06:32:16PM +0800, Erich Dollansky wrote:
> Hi Sym,
> 
> On Mon, 11 Nov 2013 09:18:36 +0000
> symbolics at gmx.com wrote:
> 
> > On Mon, Nov 11, 2013 at 04:24:00PM +0800, Erich Dollansky wrote:
> > > Hi,
> > > 
> > > I would need a documentation of the GEOM data structure. A disk got
> > > damages in a strange way during the process of backing up data. It
> > > was partitioned with gpart as all my disks using the MBR schema.
> > > When creating the backup, the system crashed. The disk was not
> > > usable anymore. I found out that the MBR was overwritten before the
> > > backup was started while the beginning of the first partition seems
> > > to be ok.
> > > 
> > > I hope to be able to recover the data saving me one week of work.
> > 
> > Hi Erich,
> > 
> > As I understand things, you believe that your filesystems are okay and
> > you just want to recreate the MBR so you can try to fsck and mount
> 
> this is the basic idea.
> 
> > them? How did you set the disc MBR up in the first place? If you used
> > the automatic scheme in the installer and you know the size of the
> 
> I used the manual way creating 6 partitions.

Do you know the sizes and order of how they were set up? They're all
UFS2 or a mixture of other things too?

> > disc, you could reconstruct things that way. What does `gpart show'
> > look like at the moment?
> 
> It does not come that far
> 
> gpart list da0
> gpart: No such geom: da0.
> 
> is all I get.
> 
> My luck is that I have three disks which are the type but manufactured
> with some months between. But their sizes differ a bit. I think that I
> should be able to recover much by just comparing the entries.
> 

You can try looking at diskinfo -v da0 to see the numbers.

I had a little play around making a test disc and mdconfig. If I get
some more time this evening I'll see if I can write a tool to scan the
disc and recover the partition data, it'd be a good exercise.

There are a few programmes in ports/sysutils you should try in the
meantime. I didn't find them useful in my tests but that might not be
indicative of anything.

--sym