How to mirror a geli partition?

[Christian Baer]

Hello Folks!

At the moment I am setting up a new machine. This has two identical
drives (Seagate Cheetah) installed. I will hold some very important data
an some very unimportant :-) data.

What I want to do is to create mirrors of those *partitions* containing
the important stuff[1]. Since the data is sensitive I also wish to
encrypt it with geli.

I've done both things before, just not in combination. And I've never
created a mirror with gmirror before. Currently I'm not even sure if I
should rather use vinum oder geom. I went for geom, because it is there
anyway because of geli. Comments about this are very welcome!

These are my main questions:

1st
The mirrored partitions will contain the same date (naturally) but the
drives however will not. It this a problem? Meaning that the mirrored partitions
on drive0 and drive1 will probably habe different positions on their
drives.

2nd
The gmirror manpage only uses full drives as providers in its examples.
I am guessing that I could also use a partition as a provider like
/dev/ad0s1d. Did I guess that right?

3rd
What happens if the partitions aren't exactly the same size? This could
happen if the partitions have different positions on the drive and I
specify the size in MB or GB. I don't care if I lose a bit of room
(meaning that the size of the smaller partition is the one that counts).
I'm just a little worried that a rounding error that makes partition0 a
few blocks larger than partition1 could cause problems.

4th
This is actually the biggest problem I am facing. In what order do I do
this? I was thinking along this way:
1 - Create partions and try to get them the same size. :-)
2 - Fill one (or both?) with random data.
3 - Make a geli provider out of one of them, newfs it.
4 - Do something like 'gmirror label -v -b load secret 1.eli'
    and 'gmirror insert 2.eli'
I am not sure if I should reverse the order of 3 and 4. Or have I gotten
the whole idea wrong?

Can someone point me in the right direction?

Regards,
Chris

[1] Backups will also be made but probably not always be up to date as
the data on these drives will change very frequently.