[linux-lvm] RFC: DM encryption target?

Christophe Saout christophe at saout.de
Fri Sep 26 08:05:17 UTC 2003

Am Fr, den 26.09.2003 schrieb jon+lvm at silicide.dk um 14:48:

> > I don't know, but couldn't the use of a one-sector block slow things
> > down because of alignment issues? Perhaps using a 4k block would be more
> > useful or storing the sector at the end of the device (like the linux
> > raid info sector).
> maybe, but does it matter? You only read the sector once, when you "open"
> the device, and write to it when you change password. During use, the real
> key is stored in memory, like any other encryption device.

No, I meant the following: Let's assume you are using crypto on a raid
0/5 device or something. Usually the filesystem uses 4k blocks. Those
blocks would normally never span across two stripes because they are
aligned. With a crypto device that uses the first sector now all
filesystem blocks get moved by one sector so that there are a lot of
blocks that span underlying stripes. A lot of harddisks these days use
internal blocks that are larger than 512 bytes so there are also
alignment issues.

That's why I meant that either this info block should be larger than one
sector or it should be moved to the end (and the linux md code does it).

Christophe Saout <christophe at saout.de>
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