Why
Now you are working with Linux on an almost empty disk.
We will add the other disks to the system.
But be carefull:
any disk you are going to add wil be formatted !
So save your data first !
How
You can insert the other disk[s], and power-up the system.
Be sure to boot from the newly installed kernel.
Alter the disk order in the Bios if necessary,
or you may make the other disks non-bootable to be sure:
Then reboot again.
When you have the other disks mounted as well, you can move your data around.
The current boot-disk is almost free, so use it.
You must at least clean 1 entire disk,
one of both that are supposed to be a boot disks.
Then you can continue installation, even with the other disk[s] missing.
Add the rest later.
Put the non-empty disks in a safe place for the moment,
and ignore them until after the installation is completed.
You're all by yourself here
So in this document,
from now on I assume you have saved all data onto the current boot-disk,
and all other disks (at least 1) can be formatted.
(the disks containg valueable dat are stored elswhere to be sure).