Re: [dm-crypt] The future of disk encryption with LUKS2

[Arno Wagner <arno@wagner.name>]

On Mon, Feb 08, 2016 at 18:26:49 CET, Sven Eschenberg wrote:
> Indeed usually a disk should be able to finish the sector write with
> remaining power. Actually most modern disks do have voltage shifters
> and most parts operate on lower voltage. 

At least for the R/W logic. The heads do not need to be
moved during a started write and the platters will keep 
spinning far longer than needed. 

> Thus a drop on the
> changer's input does not immediately lead to a drop on the output of
> the voltage shifter. If's theres enough power left for the physical
> layer scrambler and the head to write, then everything should be
> fine. 

As this depends on the buffer-capacitors, you can design how
long they keep the lower voltage (typically 3.3V or 2.5V) up
after the input has gone below, say 4.5V. With a low-drop
3.3V regulator you get about 1V of drop, before 3.3V drops.
That is plenty.

Maybe I will have a look into an older 2.5" hdd and check
when it stops spinngin and what voltage the R/W amplifier is
fed.

> I was rather wondering if there's definite sources on that?

There is not even a definite source on what error-correcting 
codes are used today or what the actual rate of non-correctable 
errors is. Disk manufacturers like to keep the user in the
dark about potential problems...

I used to look at technical manuals of disks, but in the last
10 years or so they were impossible to get, at least from public 
sources.
 
> BTW. The burst errors I mentioned did not happen on a power loss,
> but rather during operation. Reading twice, one time with burst
> errors, one time without. I checked the RAM for ages - no failures.
> That was really weird.

Indeed. Maybe you did run into a firmware error or some
PC-side controller problem that was not properly caught 
in the driver. Maybe also a DMA error or the like that
failed to move all the data into RAM. I found that 
checking alignment on such errors often gives good 
clues.

Regards,
Arno

-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno@wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
----
A good decision is based on knowledge and not on numbers. -- Plato

If it's in the news, don't worry about it.  The very definition of 
"news" is "something that hardly ever happens." -- Bruce Schneier