[dm-crypt] Advanced format (4k sector disks) and dm-crypt

Arno Wagner arno at wagner.name
Mon Jan 20 13:20:48 CET 2014


On Sun, Jan 19, 2014 at 19:07:39 CET, Garðar Arnarsson wrote:
> Thank you very much for the reply and explaination.
> I suspected that there was not a concern to dm-crypt in regards to 4K
> sectors since I did not find any mantion of it when searching the web
> and it's good to have that confirmed.

And thank you for asking! If you are not very familiar with the
lower-level mechanisms used, it is a valid queation. And the FAQ
and other documentation can only be improved when people ask 
questions.

Arno


> On Sat, Jan 18, 2014 at 7:36 PM, Arno Wagner <arno at wagner.name> wrote:
> > On Sat, Jan 18, 2014 at 20:24:47 CET, Arno Wagner wrote:
> >> On Sat, Jan 18, 2014 at 15:14:29 CET, Garðar Arnarsson wrote:
> >> > Did a quick search but came up empty handed.
> >> >
> >> > I'm wondering if there is anything special that needs to be passed to
> >> > be able to use dm-crypt (cryptsetup) with 4096 byte sector drives.
> >> >
> >> > I know md, lvm, partitions, filesystems all need to have special
> >> > triggers for 4K drives (even thouh I think it's done automatically for
> >> > all of them nowadays) but I see no mention of dm-crypt/cryptsetup.
> >>
> >> Do not worry. Dm-crypt uses 512B sectors, but there is only a
> >> negligible performance loss. This matters far, far more on the
> >> filesystem layer. If that layer does it right, dm-crypt will
> >> allways process 8 x 512B at a time, as it does process exacly
> >> what the uppeer layer requests. And alignment in LUKS is done
> >> so that 4k sectors will not be broken up for the data area.
> >>
> >> Hence this is not a concern and that is the reason it is
> >> not mentioned. I think I will add an FAQ entry for this.
> >>
> >> Arno
> >
> > Just added Item 2.17 to the FAQ.
> >
> > Arno
> > --
> > 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
> > ----
> > There are two ways of constructing a software design: One way is to make it
> > so simple that there are obviously no deficiencies, and the other way is to
> > make it so complicated that there are no obvious deficiencies. The first
> > method is far more difficult.  --Tony Hoare
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-- 
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
----
There are two ways of constructing a software design: One way is to make it
so simple that there are obviously no deficiencies, and the other way is to
make it so complicated that there are no obvious deficiencies. The first
method is far more difficult.  --Tony Hoare


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