How to safely merge two slices on harddisk?

[Malcolm Kay]

On Mon, 9 Feb 2004 13:46, Rob wrote:
> Hi,
>
> I have a hard disk, on which I would like to merge two slices
> into one single slice. The disk slices are as follows:
>
> /dev/ad1s1a    98M    43M    47M    48%    /home/userB
> /dev/ad1s1d    64G    45G    14G    77%    /home/userA
> /dev/ad1s1e   3.0G   2.5G   282M    90%    /home/userC
> /dev/ad1s1f   3.0G   1.0G   1.7G    37%    /usr/ports
> /dev/ad1s1g   3.0G   268M   2.5G    10%    /mnt
> /dev/ad1s1h   295M   295M -23.5M   109%    /diskless_swap
>
> I want to merge /ad1s1f and /ad1s1g into one 6Gb slice.
>
> The merging should NOT destroy anything in the slices before
> (ad1s1a, d, and e), but destroying the data in the one afer
> (ad1s1h) is no problem.
>
> Is there a way to do this? What is the safest one?
> (without having to backup the whole disk).

Any manipulation at this level is risky. To do so without first 
taking a backup endangers all your data.

But once you have the assurance of a backup you could copy
all the information from /mnt into some  new tree in /usr/ports.
That is a tree copy of the content of /dev/ad1s1g to a new tree
on /dev/ad1s1f.
   cp -Rp /mnt /usr/ports/newtree

Having done that partition /dev/ad1s1g becomes free and you 
can rebuild the disk label using disklabel to eliminate the 'g' 
partition and extend the size of the 'f' partitition to take up the 
extra space. But first umount the 'f' and 'g' partitions.
CAUTION
========
    Do not change the offset of 'f'. If 'g' does not physically
    follow 'f' on the disk then this is not going to work -- give up
    now!!!

If all has gone well so far you should now be able to use growfs
on /dev/ad1s1f to expand the file system to fill the partition.

Remount the 'f' partition and you should be back in business.

If you want to find what was on /dev/ad1s1g with the original path 
then
   rm /mnt
   ln -s /usr/ports/newtree /mnt

If you are on 5.x then be warned that I have no experience with 
these versions of FBSD.

And in any case I have never, myself, had occassion to use growfs.

Malcolm