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

[Arno Wagner <arno@wagner.name>]

On Mon, Feb 08, 2016 at 12:34:04 CET, Michael Kjörling wrote:
> On 8 Feb 2016 01:25 +0100, from sven@whgl.uni-frankfurt.de (Sven Eschenberg):
> > 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?
> 
> That's the theory; if a sector write is interrupted half way through
> (regardless of the reason), then the FEC data doesn't match the sector
> payload data. In this case, the difference is very likely large enough
> that the error cannot be corrected using the FEC data, so you get a
> read error back instead.
> 
> _Unfortunately_, theory and practice don't always agree. I think it
> was Google that did a study on storage errors not all that long ago,
> and one conclusion was that silent read errors (where you do get data
> back from the drive, but that data is not the same as was originally
> written), while rare, happens with a high enough probability to
> warrant consideration in large storage systems.

I think I read that paper (if so, it was pretty bad) and if I
remember correctly, they did not diagnose what the issues were,
just that they had bad data at the end in main memory.

From my experience shoveling a few hundred TBs of research data
around when 200GB disks where standard, the only undetected errors
I ever found were due to memory corruption due to a weak RAM bit 
in one server that did not have ECC memory. Those amounted to 
3 errors in 30TBs of recorded data. I never had undetected read
errors from disk (and since all data was bzip2 compressed, 
errors would have been found), so I tend to view these as not
a disk problem, but likely happening someplace after the data
leaves the disk.  

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
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