On Wed, Feb 13, 2019 at 7:06 PM Jayashree Mohan <jaya@xxxxxxxxxxxxx> wrote: > > Hi Amir! > > Thanks for putting across your thoughts on this. Your suggestions > definitely make sense, and we'll compile these information and submit > a patch for review. > > When it comes to strictly ordered metadata consistency, to the best of > our knowledge only xfs claims to provide it explicitly. In ext4, > delayed allocation and fsync of a file not persisting all its hard > links[1] are examples of violation to the strictly ordered metadata > consistency right? No, I don't think they are. At least that is not how understand what Ted wrote. > And for btrfs, they don't seem to explicit about > providing such semantics. Look at this thread[2] for example, owing to > the lack of specification, btrfs does not commit to providing such > guarantees. The discussion is not about ordered metadata, is it about what fsync(file) should do. They are related if we decide that fsync(file) should persist nlink, but I think all fs maintainers are in agreement that it doesn't matter and btrfs choice is as valid as ext4/xfs choice. That said, I don't know if btrfs does strictly ordered metadata or not. Order metadata means if user does op A then op B, you should not be able to see consequence of op B after crash without seeing the consequence of op A. Can you give a counter example for btrfs? for ext4? The different fsync() guaranties in different filesystems confuse you because if you expect fsync() to persist op B, then you expect op A to persist as well, but it may be the former (fsync) expectation that is failing and not the latter (ordered). Thanks, Amir. > > [1] https://www.spinics.net/lists/linux-btrfs/msg77340.html > [2] https://www.spinics.net/lists/linux-btrfs/msg76957.html
