http://www.howtoforge.org/replacing_hard_disks_in_a_raid1_array

RAID1の場合ですが、手順は大差ないと思います。mdadmに取り外したり、付け加えたりすることを伝える必要があります。

起動できない場合は以下を参考にしてLiveCDで起動してください。

http://advosys.ca/viewpoints/2007/04/setting-up-software-raid-in-ubuntu-server/

Boot problems

If it was the first drive that failed, after replacing it with a new unformatted drive the system may no longer boot: some BIOS only attempt to boot from the lowest numbered hard drive (e.g. sda or hda) and if it is blank the system will hang. In that case you’ll need a rescue CD capable of running a GRUB boot prompt so you can manually boot from the second physical drive.

There are many free Linux-based rescue CDs available (e.g. SystemRescueCD) but for quick access to GRUB try the Super Grub Disk. This small download can be written to bootable floppy or CDROM and give quick access to system boot tools, especially the GRUB command line.

Whatever rescue tool you use, use it to boot to a GRUB command prompt and force the system to boot from the second installed hard drive using commands similar to the following:

    root (hd1,0)
    kernel /boot/vmlinuz-whatever root=/dev/md0 ro
    initrd /boot/initrd.img-whatever
    boot

To find the correct file names for the “kernel” and “initrd” parameters, GRUB has bash-style command-line completion… type just enough of the path then press TAB to auto-complete or see a list of available choices.