[dm-crypt] Memory errors and and 3TB RAID5 partition

Arno Wagner arno at wagner.name
Wed Jan 16 12:23:21 CET 2013


Hi Frederico,

impossible to quantify, and you may also get errors in the
busses, controller and (very rare unless overclocked) CPU.

The thing about "massive file corruption" is a myth though:
Most flipped bit just lead to a flipped bit because they 
happen before encryption. Even after encryption, you lose
only one 512 byte sector per flipped bit.

What you do is, if this is critical, _underclock_ everything in
your machine by 10-20%, get ECC RAM, ensure good cooling and clean 
power. Before undercklocking, test the machine extensively at 100% 
speed or maybe even 110% or the like.

An alternative is to verify each write. Here you have to be careful
to empty all buffers and caches before doing it. That is what I
do for large files. 

Arno

On Wed, Jan 16, 2013 at 12:08:15PM +0100, Federico Foschini wrote:
> Hi all,
> I'm reading the FAQ on cryptsetup wiki because I'm plannig to set up a
> software raid 5 (mdadm) with 3 1,5TB disks and I'm a bit scared about
> memory errors.  I read that a single flipped bit can lead in a massive
> file corruption and I've got 2GB of non ECC ram on my machine... what
> is the risk of encounter a memory error writing big files (like 8-10
> GiB)?
> 
> --
> Federico Foschini.
> _______________________________________________
> dm-crypt mailing list
> dm-crypt at saout.de
> http://www.saout.de/mailman/listinfo/dm-crypt

-- 
Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
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----
One of the painful things about our time is that those who feel certainty
are stupid, and those with any imagination and understanding are filled
with doubt and indecision. -- Bertrand Russell


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