OSX - Full Disk Encryption [closed]
Your first option is FileVault which is not full disk encryption, but individually encrypts the home directories of each user:
In Mac OS X v10.4 (Tiger), FileVault stores the encrypted file system as a Sparse Disk Image, which is basically a single large file. In Mac OS X v10.5 (Leopard), FileVault stores the encrypted file system as a new image called a Sparse bundle. 1. Sparse bundles break images into smaller 8MB files called bands, allowing them to be backed up using Leopard's Time Machine feature
-- Wikipedia on FileVault
This is in addition to Disk Utility on OS X which allows you to create disk images that are encrypted individually in the same way as described above.
As was mentioned by Dave Cheney, PGP Whole Disk Encryption for OS X goes further than FileVault to actually encrypt the entire disk transparently to the OS. I use this on both my iMac (early 2008) and MacBook Air (late 2008) with OS X 10.5.x.
Encryption takes several hours, depending on the size of your disk. You can continue to use the system whilst first encryption is in progress and can restart/sleep the computer as well.
Once completed, a prompt appears before the OS X bootloader which asks for your passphrase. PGP requires you to set up a public/private key pair with which the encryption is locked to. You can add multiple keys for different users and this means that you can easily add/revoke users when necessary.
I have been using the product for almost a year now and have had no problems. OS updates run without issue and it is easy to remove the product if necessary.
Timemachine backups continue to work with the fully encrypted disk because it is transparent to the OS - the files are all accessible whilst the system is on. This means you need to encrypt your backup device(s) separately since the files will be transferred unencrypted.
It is important to note that PGP Disk Encryption does not work with Boot Camp.
You can also use it to encrypt your e-mail, iChat and external disks.
Another product I have tried is TrueCrypt which allows you to set up virtual disks that are individually encrypted. This does work on OS X but I have not used it to encrypt the full primary partition.
If you have the budget, I can definitely recommend the PGP product.
I was initially going to say, No, OS X does not support encryption of the boot drive, only you home partition via loopback mount. However some googling turned up PGP Whole Disk Encryption. I can't vouch for it as a solution as I have not tried it.
Have you tried TrueCrypt? Free open-source disk encryption software for Windows Vista/XP, Mac OS X, and Linux. I also like PGP Whole Disk Encryption like Dave.