Re: Mounting Ext3 with Ext4

[Eric Sandeen <sandeen@redhat.com>]

Matt LaPlante wrote:
> According to the Ext4 howto
> (http://ext4.wiki.kernel.org/index.php/Ext4_Howto#Converting_an_ext3_filesystem_to_ext4),
> "It is possible to mount both ext3 (and ext2, in kernels 2.6.28 and
> later) filesystems directly using the ext4 filesystem driver."  So
> this means, if I'm reading it correctly, that a kernel built with ext4
> support should be able to mount and manage ext[234] filesystems.  Is
> that correct?  If so, are there any limitations on this support?
> 
> I'm running Ubuntu Jaunty with some custom-built 2.6.29.4 kernels and
> grub2.  I seem to have no problem booting from ext4 disks, so the ext4
> support is definitely there and functioning.  I had hoped the ext3
> support meant I could build the kernel with ext4 only and carry on as
> usual with my ext3 partitions.  Unfortunately doing so causes the ext3
> partitions to fail to boot.  So...
> 
> booting ext3 with ext3 in the kernel=fine
> booting ext4 with ext4 in the kernel=fine
> booting ext3 with ext4 (only) in the kernel=not fine
> 
> Is this a problem or was it never intended to work?

It should work...

It'd be more helpful if you could include details on exactly how it
failed, but if Ubuntu builds ext4 as a module, perhaps the initrd
creation sees root as ext3 and doesn't bother to put ext4 in the initrd?

-Eric