Filesystem format for external hard disk

[Bryn M. Reeves]

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On 06/01/2012 10:06 PM, Thibault Nélis wrote:
> On 06/01/2012 04:45 PM, Bryn M. Reeves wrote:
>> Or is the ext4 code able to mount ext3 now (I didn't think so)?
> 
> I'm pretty sure it is fully backward compatible yes, even with ext2
> from what I read.  It simply doesn't use all the new and fancy
> features obviously.

Actually checking it's a fairly new feature (originally ext4 went off
on its own for quite a while to avoid unsettling the older exts). It
was added upstream a couple of years ago:

commit 24b584240a0006ea7436cd35f5e8983eb76f1e6f
Author: Theodore Ts'o <tytso at mit.edu>
Date:   Mon Dec 7 14:08:51 2009 -0500

    ext4: Use ext4 file system driver for ext2/ext3 file system mounts

And it was turned on in the Fedora kernels for f16:

* Thu Jul 21 2011 Chuck Ebbert <cebbert at redhat.com>  3.0-0.rc7.git10.1
- - 3.0-rc7-git10
- - Use ext4 for ext2 and ext3 filesystems (CONFIG_EXT4_USE_FOR_EXT23=y)

I'd not noticed it before as none of this gets built as modules now so
you don't see the separate lsmod entries.

Regards,
Bryn.
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