The file system is not “truncating” files. The application is truncating the files, or is constantly overwriting the files using the rename system call. This is a fundamentally unsafe thing to do, and ext3 just happened to paper things over.
Theodore Ts’o in a bug comment on how data loss can occur on Ext4. Knowing how the file system works is what separates real programmers from people that hack things together (i.e. people like me). By way of Jeremy Zawodny.
1 year ago