disklabel disappeared after power loss

[Mikhail Teterin]

Thank you very much for the quick response!

> > After a sudden power loss, one of the disks (ad2) can not
> > recover.

> What does `fdisk ad2' say?

Some nonsense -- as if I had only a 30Mb partition-4...
 
> What does `disklabel ad2' say?

Something about "amnesiac" with only the c-partition.

I used /stand/sysinstall to create a small swap partition at the
beginning of the drive. I don't know, what it does, but it re-created
the label, which I was then able to edit with disklabel.

scan_ffs (from the sysutils/scan_ffs) helped me recover the exact size
and offset. I wish, fsck had scan_ffs' functionality built-in...

> Maybe something is messed up, so that disklabel does not dare to
> write a new disklabel.

Well, sysinstall did not mind...
 
> Is something from ad2 mounted read-writeable, when you get the "Op
> not perm" error?

No, definetly not.

> How about
> 1. copying the data from the former ad2e into another filesystem,

This is a 50% full 180Gb disk. The only other disk nearby is a 20Gb
system drive...

> 3. establishing an all new disklabel with proper ad2e? :-)
> (most likely ad2e is too big?)

ad2e was not too big -- it did not exist. But sysinstall did the job.
Perhaps, disklabel needs to learn a few tricks from that tool.

And, of course, the main question is, why could the label disappear as a
result of something as mundane as powerloss?

Yours,

	-mi