Re: [gentoo-dev] Warn users not to do separate /usr partition without proper initramfs in the handbook?

[Rich Freeman]

On Tue, Aug 2, 2011 at 4:02 AM, Michał Górny <mgorny@g.o> wrote:
> BTW doesn't encrypting rootfs require initramfs anyway?
>

Yup.

On a side note.  I've been experimenting with Dracut+LVM+RAID5 and
have found that it actually works pretty transparently.  Now, I
haven't tried it with /usr not on the rootfs - I can tell that Dracut
is definitely parsing my /etc/fstab to mount my root, but I'm not sure
if it tries to mount anything else by default.  It is fairly slick -
it mounts root any way it can read-only to get to the fstab, and then
remounts it following the options in fstab.  (Which means that you
need to make sure fstab is accurate since it actually gets used for
the rootfs now.)

I also found that the dracut initramfs is MUCH faster than the
genkernel one - it does a good job of only loading drivers necessary
to find the root, and it can take hints to speed that up.  It also
required less configuration - the only required kernel parameter even
for mdadm+lvm is root= (which takes device, UUID, or label).

I got it working with an old-metadata /boot (probably need to mess
with grub v2 to avoid that, assuming that even works), and then
everything else including root on mdadm-raid5+LVM.

So, my feeling is that while we should support minimal (ie
non-gnome/etc) configurations that follow FHS and don't require an
initramfs, I don't really see leveraging dracut as a big problem as
long as we update our documentation to make the preferred approach
clear.

Everybody should also read that Fedora link earlier in the thread:
http://fedoraproject.org/wiki/Features/UsrMove

I'm not suggesting that we should do this, but this does seem like a
legitimate use-case.  It is a bit more suited to binary distros with
release cycles, but I could see in a datacenter how it might be nice
to NFS-mount just about everything including /usr, /bin, /lib, etc.
Such a setup would actually be pretty easy to accomplish with Gentoo -
in theory you can just create symlinks for the various root
directories into /usr and let the package manager install the files
into them.  In practice it might run into issues (I know that symlinks
for some of the top-level directories were not liked by some of the
package managers in the past - I had to use bind mounts to accomplish
this, and that might be a better solution though I have no idea if
Dracut can figure that out in fstab).

Rich