How to choose LUKS encryption when installing RHEL 6?

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http://unix.stackexchange.com – With the default RHEL 6 installer, how can I choose the LUKS encryption? Afaik if I prepare the disk like cryptsetup luksFormat -c cast5-cbc-plain -s 128 /dev/$DEVICE could be the "fastest" encryption, but the installer only prompts for password, then later, at the partitioning it recognizes it as "unknown" partition. (HowTos)