LXer: Possible data loss in Ext4
 

Published at LXer:

A bug report posted in the bug tracker for the next version of Ubuntu 9.04 (Jaunty Jackalope) describes a massive data loss problem when using Ext4, the future standard file system for Linux, available as an option when installing Ubuntu 9.04. The report describes a crash occurring shortly after the KDE 4 desktop files had been loaded, resulting in the loss of all of the data that had been created, including many KDE configuration files.

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Note that this data loss is not something out of the ordinary, it also can happen with XFS, and for the same reason. It all has to do with 'delayed allocation', which basically writes data to RAM first, then later on (up to 1 min later) it writes it to the disk. If your machine crashes within that window, then the data you were manipulating is corrupted or lost.

Conclusion:
Switch to JFS :)