[Discuss] TrueCrypt with SSD

[Edward Ned Harvey]

> From: Ben Eisenbraun [mailto:bene at klatsch.org]
> Sent: Friday, August 19, 2011 10:50 PM
> 
> On Fri, Aug 19, 2011 at 10:41:04PM -0400, Edward Ned Harvey wrote:
> > As I said, and others have said the same thing, the most cpu overhead
> > you'll see, depending on your processor and the encryption algorithm, is
> > 1%, 3%, 20%, 30%...
> 
> 20-30% extra CPU usage on a laptop for disk operations puts a serious dent
> in your battery life.

That's true.  The question is whether it's a price you're willing to pay.

Something people don't necessarily realize though...  Suppose you have the
AES instruction set and we're only talking about 1% cpu utilization or
something ridiculously low.  That's not insignificant because it's still
doing the same amount of work.  It's just doing that work faster.  The % cpu
utilization is based on time, not based on power.  You could sit there in a
while loop, consuming 100% cpu and consuming basically nothing for power,
because you're only toggling the bits in such a tiny area of the processor.
Or you could use 1% cpu for more complex operations and consume far greater
power.

The same thing is true for all your other operations.  You've got a GPU that
does all your fancy graphic effects.  Aero and Aqua, transparency,
animations, drop shadows, 3D rendering, etc etc blah blah.  If you disable
these features you'll save power.  Keep you windows in one place on the
screen.  Stop minimizing them, or switching to different desktops.  If you
use http instead of https, you'll save power.  Telnet versus ssh.  FTP
versus SFTP or FTPS.  Guess what?  Your antivirus is pretty significant.
All that pattern matching, etc...

What are you willing to pay for?  In terms of battery usage.   ;-)

Out of all the above, which one consumes the most power?  Of course it
depends on what you do.  Most of the time your disk is idle, so with or
without encryption, most of the time it doesn't make a difference.  Your
screen is always on.  Dimming your screen and avoiding compute-intensive
workloads and graphic-intensive workloads are still the most effective
things you can do to save power.

If you have a HDD, and no encryption, then the drive consumes essentially
the same power regardless of whether or not it's doing anything.
If you have a SSD, it consumes essentially no power when idle, consumes a
little bit during reads, and consumes a lot during writes.  SSD's during
writes burn more power than an HDD in any state.
If you have encryption enabled on either one, then there is an additional
power tax to consider...  Writes cost more, reads cost less, but both are
nonzero.