This tutorial describes how to rescue data from a single hard disk that was part of a LVM2 RAID1 setup like it is created by e.g the Fedora Core installer.
Read about it at howtoforge
Why is it so problematic to recover the data? Every single hard disk that formerly was a part of a LVM RAID1 setup contains all data that was stored in the RAID, but the hard disk cannot simply be mounted. First, a RAID setup must be configured for the partition(s) and then LVM must be set up to use this (these) RAID partition(s) before you will be able to mount it. I will use the Knoppix Linux LiveCD to do the data recovery.