[dm-crypt] Hybrid drives

[Heinz Diehl]

Hi,

I just took a closer look at one of the (new?) hybrid harddisk drives,
such as the Seagate Momentus XT, and now I'm wondering if this 
is a top level security problem. If I understand it correctly, the 4 GB
SSD memory on the harddisk operates independendly of the drive itself,
acting as a buffer/cache for virtually all the data stored to the drive. Some
logic in the harddrives controller is going to serve the 4 GB SSD memory
part, which is not available/accessable to the OS.

In other words: such hybrid drives can not safely be encrypted with
LUKS/dmcrypt (or any other WDE software), because the controller 
randomly swaps out 4 GB data to the SSD area, and even after shutting 
down the machine, parts of/the whole LUKS header/key could possibly 
be left on the SSD part?

( http://www.youtube.com/watch?v=nX_WyOhTQEw&feature=related )