Speed is too importantFor whom? For me data consistency is much more important. Before barriers were supported, we ran ext3 on IDE disks without write caching, and that's really slow. The file system was still fast enough.
Stephen Tweedie didn't make data=journal the default, either.Actually he did, at least at the start. Later it got changed (by whom?) to data=ordered; that still has the potential to provide data consistency unless existing files are overwritten.
As for an example: Consider a process writing file A and then file B. With ext4 I expect that it can happen that after recovery B is present and A is not or is empty. With ext3 I expect that this does not happen. But given that I did not find any documented guarantees in Documentation/filesystems/ext3.fs, maybe we should lump ext3 with tmpfs, too.
Still, my search brought up a Linux file system that gives guarantees: In nilfs2.txt it says:
order=strict Apply strict in-order semantics that preserves sequence of all file operations including overwriting of data blocks. That means, it is guaranteed that no overtaking of events occurs in the recovered file system after a crash.Yes, that's exactly the guarantee I want to see. This means that any application that keeps its files consistent as visible from other processes will also have consistent files after an OS crash.
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