Creating a software RAID1 setup with one 2TB and two 1TB drives isn't difficult, but in this case the setup was running in production as a RAID1 over two 1TB drives. Small sda1 and sdb1 partitions form /dev/md0 and are formatted ext3 for /boot. Large sda2 and sdb2 partitions form /dev/md1 and are an LVM PV, the rest of the system is formatted in logical volumes. Target situation: to have /boot on all three disks, and the LVM volume group as large as possible, redundant on mirrorred diskspace. The procedure is strict, but straightforward: partition the new disk in 3 partitions (small - large - large) make md0 3-legged with sdc1 as the third device make md1 3-legged with sdc2 as the third device wait for the sync (watch /proc/mdstat) remove sdb2 from md1 and make it 2-legged again (you'll have to --fail sdb2 before you can --remove it). make a new md2 device for sdb2 and sdc3, make it a PV and add it to your volume group. The only utilities needed are cfdisk, mdadm, and lvm (for ...
plenty of grains to pick