Re: EXT3

[Craig Dickson <crdic@yahoo.com>]

Raffaele Sandrini wrote:

> Everywhere i hear about ext3!
> 
> What is that? What are the advantages (disadvantages)? How can i
> set it up on Debian?

Ext3 is a journaling filesystem, which means that it applies
database-style transaction logic to the filesystem for improved
reliability in the face of sudden failures (e.g. power loss). It is an
extension of ext2 and is compatible with it. You can convert an ext2
filesystem to ext3 simply by creating the journal inode on it. You can
convert an ext3 filesystem back to ext2 simply by removing the journal
inode (as long as the journal doesn't have any pending transactions in
it).

To use ext3, you need a kernel that supports it. Patches for 2.2.19 and
the current 2.4 kernels are available online. Also, Alan Cox's current
2.4 kernels (the -ac kernels) include ext3 support.

Patches for recent 2.4 kernels may be found here:

    http://www.uow.edu.au/~andrewm/linux/ext3/

There is an ext3 FAQ, with pointers to patches for Linux 2.2.19, here:

    http://people.spoiled.org/jha/ext3-faq.html

Once you have an ext3-enabled kernel running, you can convert ext2
filesystems to ext3 with this command:

    tune2fs -j /dev/hda1

(substituting the appropriate partition for /dev/hda1). If you do this
while the partition is mounted, you will see a file called .journal in
the root directory of the partition. If you do this while the partition
is unmounted, the journal inode will be invisible. Other than that minor
detail, it doesn't really matter whether the partition is mounted or not
when you convert it.

Craig