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From: Alexandre Oliva
Subject: Re: BTRFS, LVM, LUKS
Date: Sat, 06 Jul 2019 16:23:02 -0300
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

On Jul  5, 2019, Giovanni Biscuolo <address@hidden> wrote:

> With BTRFS multi device activation is built in the Linux kernel AFAIU,

I'm pretty sure btrfs dev scan or similar must introduce each of the
filesystem components to the kernel before the kernel will use them.

> I cannot help much with mdraid since I still had not the chance to
> study how device-mapper devices are activated

There used to be in-kernel scanning in mdraid, but I recall the plan as
of 15+ years ago was to phase that out and take care of it all in

>> and any recursive combinations of mdraid, dmcrypt, etc?

> Recursive? Do you mean LUKS on mdraid on LUKS?

Well, LUKS doesn't make much sense to duplicate indeed, though there's
no reason to prohibit it (say, one could be mirroring a fully-encrypted
disk onto a logical volume that's fully encrypted itself), but building
volume groups or raid components out of logical volumes is occasionally
useful, even when the logical volumes are backed by other raid devices.

> Filesystems can have dependencies on other filesystems or mapped-devices
> (see "dependencies" member of file-system)

> I hope this clarifies how Guix assemble its filesystems.

To some extent.  I meant to ask about the dynamics during boot-up rather
than the static description in the configuration, but that's very useful
information to get me going in a not too distant future.

(I'll be too busy with other stuff, like finishing a new lecture to be
delivered by the end of the month, to jump into this right away; I
wanted to, in order to use guix to deliver the speech, but I doubt I'm
going to be able to make the jump in time ;-(

Alexandre Oliva, freedom fighter  he/him
Be the change, be Free!                 FSF Latin America board member
GNU Toolchain Engineer                        Free Software Evangelist
Hay que enGNUrecerse, pero sin perder la terGNUra jamás - Che GNUevara

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