Ext4

Ext4 is an improved filesystem for Linux, introduced in kernel 2.6.28. Previous kernels had development implementation (i.e. experimental). For more information about Ext4, follow the links in the See Also section.

Compatibility:

Old Debian releases don't support Ext4 (i.e. Lenny and earlier).
Ext3 filesystems can be upgraded to Ext4 (but not the other way around).
It is not possible to mount Ext4 with Ext3 (with some exception. read this article).

Status

Ext4 in Squeeze, testing and Unstable

Upstream kernels since 2.6.28 (which has a serious resize bug) officially supports Ext4 in production environments.
Ext4 is currently in Debian Installer.

Ext4 in Lenny

Debian Lenny doesn't support Ext4 (kernel 2.6.26) because it was still an experimental feature during the development of Lenny. Still, Lenny's 2.6.26 kernel provides the development module ext4dev. (see the FAQ)
The ext4 wiki Debian entry says in reference to Lenny 'you should mount ext4dev filesystems using -o nodelalloc and only use freshly created filesystems using "mke2fs -t ext4dev"' . Making ext4dev appears to set the test_fs flag, but the nodelalloc option doesn't work: EXT4-fs: Unrecognized mount option "nodelalloc" or missing value.

FAQ

How to mount an Ext4 filesystem under Lenny

Lenny doesn't really/officially support Ext4 (because it's experimental in its kernel version). Still, you can try to mount an Ext4 filesystem in read-only mode... and see what you see !

tune2fs -E test_fs /dev/XXX
mount -t ext4dev -o ro /dev/XXX /mnt/ZZZ

How to convert Ext3 to Ext4

See https://ext4.wiki.kernel.org/articles/e/x/t/Ext4_Howto_d00b.html

Status

Ext4 in Squeeze, testing and Unstable

Ext4 in Lenny

FAQ

See also