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

Arno Wagner arno at wagner.name
Mon Feb 8 17:41:43 CET 2016


On Mon, Feb 08, 2016 at 01:25:31 CET, Sven Eschenberg wrote:
[...]
> Concerning disks, I thought with ACS2/ATA-8 real write barriers were
> introduced. On the other hand I've seen disks returning successfull
> reads with long zero-burst-errors undetected - no fun. I always
> wondered how a HDD exactly behaves when power fails, while a sector
> is in transit. My best hope is, that the CRC at the end of the
> sector does not match and an error is returned on the next read?

For these you should have intact data on disk, but
your data never made it there. If data after the zeros
did get written fine, there is a simple explanation:
Modern disks may reorder sectors in order to be able
to begin writing as soon as the heads are stable in 
the track.

Behavior on power failure used to be that the disk will 
notice the power failing early enough that it has enough 
time left with hood power to finish a sector-write in 
progress. I think that still applies. The zeros would 
then be sector-aligned and/or the data that was in 
those sectors before, hence the checksums are fine.

The thing is that in a typical PC, power drops relatively 
slowly and disks work non-seeking for a lower voltage
that the thresholds. Add to that that a single sector
write takes less than 1ms (probably much less), and
you get ample time to finish a write in progress.

Regards,
Arno

-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at 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


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