We had a disk failure on one of our Xen servers at work last week, and what we thought would be a quick disk replace, turned into a small nightmare. Our setup is fairly “simple”: 2 x raid1’s consisting of sda1/sdb1 (/dev/md0 mounted at /) and sda3/sdb3 (/dev/md1 with LVM on top of it). mdadm reported that sdb1 and sdb3 had failed, so we just had to identify which disk was sdb in the server and replace it.