Users of the Kubuntu recently suffered data loss while using the new ext4 file system. It happens when there is a power loss or a system failure. Note that this is not specific to Kubuntu. The Kubuntu users were just the first to try out the new file system.
I’m not talking about data that you’ve just written to a document or application. These failures are returning 0 byte files on any application that has a write to a file. That is to say that your data is completely gone, not just the unsaved part.
Developer of the ext4 file system, Ted Ts’o, has joined into discussions to explain what is going wrong. He has this to say: “The short answer is (a) yes, I’m aware of it, (b) there is a (partial) solution, (c) it’s not yet in mainline, and as far as I know, not in an Ubuntu Kernel, but it is queued for integration at the next merge window, after 2.6.29 releases, and (d) this is really more of an application design problem more than anything else.”
The problem is a write commit issue. The ext3 file system committed writes within 5 seconds. In an effort to enhance security and speed Ts’o increased the data commit to 60 seconds on the ext4 file system.
So far as the application design comment he apparently is asking developers to redesign their applications to deal with the 60 second delay. While this may happen over time it is certainly not going to be something that happens in the immediate future.
My advice is to leave the ext4 file system alone until it becomes mainstream and matures. There is obviously quite a bit of work still to be done before it is production ready for servers or workstations.