Ext4 Howto

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General Information

As of this writing (mid-July, 2008, just after the release of 2.6.26), the ext4 code is functionally complete and functional enough that a few people are using it in production. However, it is still being tested and although the developers haven't lost any data yet, please be cautious and keep plenty of backups!

The ext4 developers can be contacted at the ext4 mailing list. They are sometimes also can be found on IRC.

Getting Ext4 code

For people who build their own kernel

1. Start with a 2.6.26 kernel. Optionally apply the 2.6.26-ext4-1 patchset to get improved performance through delayed allocation. In your kernel's .config file, enable EXT4DEV_FS (along with EXT4DEV_FS_XATTR and EXT4DEV_FS_POSIX_ACL if you like).

2. Compile the latest version of e2fsprogs (as of this writing 1.41.0) from kernel.org or from Sourceforge.

For people who are running Fedora

Fedora Core 9 has a kernel based on 2.6.25 that has basic ext4 support. (It is missing some of the latest fixes and performance optimizations, such as delayed allocation.)

There is a Yum repository with an updated e2fsprogs (and updated kernel?) available. XXX need location and more detail

Creating ext4 filesystems

Creating a new ext4 filesystem is very easy once you have upgraded to e2fsprogs 1.41 or later. Simply type:

       $ mke2fs -t ext4dev /dev/DEV

Once the filesystem is created, it can be mounted as follows:

       $ mount -t ext4dev /dev/DEV /wherever

Converting an ext3 filesystem to ext4

To convert an existing ext3 filesystem to use ext4, use the command

$ tune2fs -O extents -E test_fs /dev/DEV

If the filesystem was created with 128 byte inodes, it can be converted to use 256 byte for greater efficiency via:

       $ tune2fs -I 256 /dev/DEV

WARNING: Once the extent feature has been turned on, the filesystem will no longer be mountable using the ext3 filesystem!

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