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

Ralf Ramsauer ralf at ramses-pyramidenbau.de
Wed Jan 16 12:24:47 CET 2013


Hi,

i have a 4x3TiB Raid 6(because it's expandable) setup using a md-raid +
dm-crypt + LVM.
Up to now, i never had any problems with it.

A friend just told me, that SATA has an error rate of about 1 Bit each
3TiB of transmission,
so a bit is written written or read wrong(but i don't know if this is
correct).
Worst case, one error bit leads to a corrupt raid sector(Raid 5 is able
to detect the corrupt
sector, but Raid 5 won't be able to correct it, correct me if i'm
wrong). This corrupt sector
could lead to a corrupt dm-crypt sector, which leads to an corrupt LVM
sector, and so on.
Finially, your filesystem could get broken.

So think about using large partition with encryption.

I never had trouble with my setup, but now I would set it up in some
other way.

Here's a nice article about it:
http://subnetmask255x4.wordpress.com/2008/10/28/sata-unrecoverable-errors-and-how-that-impacts-raid/
--
Ralf

On 01/16/13 12:08, 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



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