Arch Linux: LVM on top of an encrypted partition

Introduction
Here, I’m describing how to set up full disk encryption using dm-crypt combined with logical volumes with Arch Linux. Most people use encryption to avoid physical access to their data by people who aren’t explicitly allowed. It makes quite much sense to set up encryption at a notebook in case it’s getting lost or stolen - the finder/thief has the hardware but not your data! For this scenario, it is not necessary to have all copies of that data encrypted because you usually keep the copies on a safe place (i.e. if you are using a home server for backups). In the other case, if you explicitly don’t want anybody to access your data at any time at any place you have to make sure that all copies of the data are either erased or stored encrypted. Also don’t forget: A running system which uses full disk encryption is still vulnerable to network/Internet attacks!

There are two ways of setting up an encrypted disk using LVM:
1. Create the LVM and encrypt every volume separately
2. Set up LVM on top of an encrypted partition
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