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Soft updates were available and documented here: http://www.netbsd.org/docs/misc/#softdeps

Yes...but not in the same way other people do journaling. Apparently they've metadata journaling - just like XFS, JFS or ext3 with the "data=writeback" mount option.

But if you only journal the metadata, you're only sure that the metadata is safe - not the data. IOW, you don't get metadata corruption (you don't need to fsck after a hard reboot), but the data of the file you were writting at the time of the reboot can be lost/corrupted. In XFS for example a file can get completely zeroed after a hard reboot.

There're two main ways to workaround this. One, journal the data (like in ext3 with the data=journal option) - but it's too slow. Second, write the data of a file before you journal its metadata, so that even in the event of a hard reboot, you are sure that the content of the file are not corrupted/lost - they may be outdated (the data was in ram and was not written to disk when the reboot happened), but not lost/corrupte (you may get a "corrupted" file in the sense that the process which was writting to it doesn't finishes writting what it was doing, but certainly you don't get rubbish). This is what ext3 does by default - it harms performance, but it's worth of it, specially for desktops.

You can also avoid completely the journaling, like zfs/btrfs do, but that's not really a "journaling mode"

it says in the announcement to remove "softdep" if presnet.



Edited 2008-08-01 17:25 UTC

Soft-updates and the log-structured filesystem (LFS). But soft-updates are fairly complex, and LFS does not have the same proven reliability as FFS. So, the addition of journaling to FFS is great, and a very nice contribution from Wasabi!