Encrypting a disk that has stuff on it?
Not doing backups is crazy and scary given that your data is business/mission critical and not your movie collection. So whatever you do, backup your data. Consider the following scenario: you're performing the encryption and during the encryption process you have a power failure on the power grid. In that case you would will lose a lot, if not all your data.
So invest the time to backup - even if you have to backup over a 56k line, it's worth the time.
Regarding which tool to use, see the other answers.
Don't do it!
it's a bit too much data for backing it all up before encryption.
This seems to indicate that you would only back up to protect against loss during encryption. Everyone is answering your question, but this the the elephant in the room.
If you care about this data you need to back it up!
Until you do that, don't even think about encrypting or doing anything (and RAID N, for all values of N, is not backup).
- Hard drives are physical devices that fail.
- Hard drives are physical devices that fail.
- Hard drives are physical devices that fail.
(let alone the thousands of other ways to lose irreplaceable data)
I've used TrueCrypt http://www.truecrypt.org/ for whole disk encryption in the past for Windows and Linux.
Bruce Schneier has written articles about getting past whole disk encryption including these two:
- Evil Maid Attack - http://www.schneier.com/blog/archives/2009/10/evil_maid_attac.html
- Cold Boot Attacks against Disk Encryption - http://www.schneier.com/blog/archives/2008/02/cold_boot_attac.html