Create a mirror on disk with valid data

[Victor Sudakov]

Victor Sudakov wrote:
> > 
> > I have only ever mirrored disks with data on them.  Its a question of
> > bootstrap - does the mirror comes first or does the data you are going
> > to mirror come first?
> 
> Suppose the disk has valuable data in the last sector and you are
> going to create a mirror from this disk. What is going to happen when
> the last sector is overwritten with the mirror metadata? Your data will
> be lost, right? Suppose you need to access the last sector, access
> will be denied, right?

I have done some experimenting and found out the following. If you
plan to put data onto a disk first, and convert the disk into a mirror
later, the disk should be from the very beginning labelled so that the
area for data is one sector smaller than disklabel suggests. If this
condition is met, I believe converting a disk with data into a mirror
is safe.

-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN