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

[Arno Wagner <arno@wagner.name>]

On Mon, Feb 08, 2016 at 05:32:14 CET, Sven Eschenberg wrote:
> 
> 
> Am 08.02.2016 um 04:43 schrieb f-dm-c@media.mit.edu:
> >     > Date: Mon, 8 Feb 2016 03:46:27 +0100
> >     > From: Sven Eschenberg <sven@whgl.uni-frankfurt.de>
> >
> >     > If a sector fails, it is not that uncommon that a whole chunk of
> >     > consecutive sectors fail (for rotating disks that is).
> >
> >Oh, come on.  A one-meg gap is 256 4K sectors and 1024 1K sectors.
> >
> >I've never seen anything take out more than a handful of sectors
> >adjacent to each other unless the disk has completely failed.
> >Anything that's chewing up multiple megs or tens of megs at the start
> >of your FS is likely to destroy any other random parts of it as well.
> >
> >Okay, how about a -10- meg gap?  That enough?
> 
> Well, I've seen several thoundand adjacent sectors going down. And
> not just once.

Same here.
 
> As I pointed out creating a filesystem can easily destroy both
> headers, even though many FSes have a rather thin metadata
> structure. Another neat example mdadm - default is header at 4k
> (primary header will be damaged) followed by a bad block list and
> and intent bitmap. The size of those can vary afaik.
> 
> To be honest, I am not completely sure what a good offset would be.

I like the end, because it is clear and far away. It is also what
md-RAID for superblock 0.90 does.

Non-redudancy during resize is not an issue, as anybody sane will 
only resize with a header-backup done before. Insane people will 
manage to screw up anyways, nothing we can do about that. Resize
is a dangerous operation, no way around that. We can prevent
people from hosing their LUKS container when creating filesysems
on it though, or partition sectors or the like.

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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