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Kernel Hackers On Ext3/4 After 2.6.29 Release
microbee writes "Following the Linux kernel 2.6.29 release, several famous kernel hackers have raised complaints upon what seems to be a long-time performance problem related to ext3. Alan Cox, Ingo Molnar, Andrew Morton, Andi Keen, Theodore Ts'o, and of course Linus Torvalds have all participated. It may shed some light on the status of Linux filesystems. For example, Linus Torvalds commented on the corruption caused by writeback mode, calling it 'idiotic.'"
This is a potential problem when you are overwriting existing bytes or removing data.
In that case, you've removed or overwritten the data on disk, but now the metadata is invalid.
i.e. You truncated a file to 0 bytes, and wrote the data.
You started re-using those bytes for a new file that another process is creating.
Suddenly you are in a state where your metadata on disk is inconsistent, and you crash before that write completes.
Now you boot back up.. you're ext3, so you only journal metadata, so that's the only thing you can revert, unfortunately, there's really nothing to rollback, since you haven't written any metadata yet.
Instead of having a 0 byte file, you have a file that appears to be the size it was before you truncated it, but the contents are silently corrupt, and contain other-program-B's data
Well, some Linux filesytem developers (and some fanboys) have been chastising other (higher-performance) filesytems for not providing the guarantees that ext3 ordered move provides.
Application developers hence were indirectly educated to not use fsync(), because apparently a filesystem giving anything other than the ext3 ordered mode guarantees is just unreasonable, and ext3 fsync() performance really sucks. (The reason why you don't actually *want* what fsync implies has been explained in the previous ext4 data-loss posts).
Some of those developers are now complaining that their "new" filesystem (designed to do away with the bad performance of the old one) is disliked by users who are losing data due to applications being encouraged to be written in a bad way, and telling the developers that they now should add fsync() anyway (instead of fixing the actual problem with the filesystem).
Moreover, they are complaining that the application developers are "weird" because of expecting to be able to write many files to the filesystem and not having them *needlessly* corrupted. IMAGINE THAT!
As an aside joke, the "next generation" btrfs which was supposed to solve all problems has ordered mode by default, but its an ordered mode that will erase your data in exactly the same way as ext4 does.
Honestly, the state of filesystems in Linux is SO f***d that just blaming whoever added writeback mode is irrelevant.
You forgot to include a link to the comment you'll be writing later.
Maybe the power failed in the middle of him writing his comment?
Don't worry...it'll appear in some other Slashdot thread until CmdrTaco does a fsck.
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