Finish fsck.nilfs2

[madroach]

Fsck for nilfs2 is still missing.

It would be nice to have some more information what this means for the reliability and recoverability of the fs.

The FAQ states:

• Quick crash recovery on-mount

which seems to suggests a fsck is not really needed ?

[konis]

Sorry for the insufficient explanation.
That doesn't mean that fsck isn't needed.

nilfs2 uses filesystem checkpointing to ensure that data written synchronously is recorded and that the filesystem can be mounted with consistent data and metadata even in the event of a sudden power failure or system reboot (1).

However, recovery is not possible in the following cases:
(2) Metadata corruption due to a bug in NILFS2 itself
(3) Metadata corruption due to bit corruption, resulting in a filesystem error
(4) Data corruption at the block device level due to SSD lifespan or physical damage to the recording media
(5) A block device is intentionally or accidentally overwritten

At least in cases (2) and (3), fsck would correct the metadata and hopefully salvage as much user data as possible. However, nilfs2 guarantees recovery without fsck only in case (1).

The fact that fsck is not yet included is a result of a lack of development effort (and activity) on this project, and as one of the project's founders, I have no excuses for that.

The web page's statements about the reliability of this filesystem may sound a bit exaggerated. If you're happy with the above statement, I'd like to clarify this on the web page and be more honest about its status.