RAID upgrade

I have filesystems on LVMs on RAIDs on partitions. Updating a disk is then, arguably, rather non-trivial. These are my notes-to-self. Maybe they'll help you too?

My setup:

# cat /etc/debian_version 
lenny/sid
# uname -a
Linux falcon 2.6.18-6-amd64 #1 SMP Mon Jun 16 22:30:01 UTC 2008 x86_64 GNU/Linux
# mdadm --version
mdadm - v2.5.6 - 9 November 2006
# lvm version
  LVM version:     2.02.07 (2006-07-17)
  Library version: 1.02.08 (2006-07-17)
  Driver version:  4.7.0

Hot removing a disc from a raid1

(spares already available)

mdadm --fail /dev/md0 /dev/sda2
mdadm --remove /dev/md0 /dev/sda2

You can watch the spares take over with

cat /proc/mdstat

This process starts immediately after the --fail.