[dm-crypt] LUKS safety on RAID 1 mirror

Arno Wagner arno at wagner.name
Tue Nov 25 15:18:52 CET 2014


On Tue, Nov 25, 2014 at 11:03:17 CET, Mark Connor wrote:
> Hello
> I currently have a deployment with luks (aes-cbc-256) on different 1TB, 500GB, 300GB etc. drives. All the drives use different keys and XFS filesystem on the top of luks. 
> I'm planning to replace this setup with 2X4TB disks in software raid1 (with mdraid) but I have my concerns.

> 1, If a sector goes bad on disk1 that normally shouldn't be replicated to
> disk2 but in case of luks I don't know what happens then.

LUKS changes exactly nothing compared to the normal behavior of
the raid. That is why things like RAID, LUKS, etc. are layered.
> 2, I think it is more practical -when one is dealing with encryption- to
> keep many smaller partitions encrypted with separate keys, in case of
> partial disk failure (other parts of the disk can still be accessed).

No. The only valid reason for different keys is security. It has
no application with regard to reliability.

> Also all the partitions have their own separate luks headers...
> Unlike if I don't even create partition just put sda (4TB) sdb(4TB) into
> and md0 array and make luks on that one, if anything goes wrong with the
> header I lose all my data or if any part of the disks breaks.

Same as always. The probability per time goes down a tiny bit, but 
almost all damaged headers are due to user error and a few are due 
to faulty software, and in both cases RIAD changes exactly nothing.

> I know that ultimately raid is only protect against drive failures (not if
> files get corrupted or deleted) so have to have a separated snapshotted
> backup next to it.  But would implementing raid1 in case of luks be an
> advantage or a disadvantage?

No impact. You still need backup, and all LUKS installations 
where the data has any worth should have a header backup.

Relevant information is also in the FAQ, Section 6 and Items 2.2,
2.8 and 5.7.  I suggest you have a look.


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

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"news" is "something that hardly ever happens." -- Bruce Schneier

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