# [arch-releng] [archiso] saying good-bye to union-fs-method?

Gerardo Exequiel Pozzi vmlinuz386 at yahoo.com.ar
Tue May 31 11:08:52 EDT 2011

On 05/31/2011 07:54 AM, Thomas Bächler wrote:
> Am 31.05.2011 03:21, schrieb Gerardo Exequiel Pozzi:
>> Hi
>>
>> * With 2.6.39 there is no aufs2 support, at least for a long time[#1].
>> * I think that back in time with unionfs is not desirable, needs a
>> complete kernel patch.
>> * union-fs-fuse does not work good.
>>
>> What about using the method like in Fedora? (basically a device-mapper
>> with a snapshot in tmpfs).
>>
>> This change from file-to-file level to block-to-block logic.
> This actually sounds pretty cool. However, I don't understand how it
> works: The squashfs file system is a read-only one, how can we put that
> into a block-level snapshot?
>
Yes, but there are at least one downside: since is not an union-fs,
there is no concept of layers. We are currently using "overlay" thats
overlap some files on the layer "root-image". With the others layers
like "core-pkgs" and "lib-modules", there are no overlap and can be
replaced by a simple mount point.
Of course this "overlay" can be merged at build time on "root-image".

image of and 4 GiB ext4. There is another small squasfs image with
another one file inside that is a "lvm snapshot". So dm device is made
via these images loopback mounted...

The code is here
http://git.kernel.org/?p=boot/dracut/dracut.git;a=tree;f=modules.d/90dmsquash-live

--
Gerardo Exequiel Pozzi
\cos^2\alpha + \sin^2\alpha = 1