Re:Don't forget the cache (Score 2)

No one's forgetting the cache. The whole point of this is that it's a way to deal with the fact that filesystem caching creates a disparity between the os-view of the file system and the actual state of the filesystem on the disk. Instead of just dirtying and writing individual pages willynilly, we keep an idea of "snapshots" (not to be confused with NetApp snapshots...) of the whole filesystem, and we ensure an entire snapshot of the filesystem is written out to disk atomicly, not just single blocks/pages. So we don't guarantee the contents of your files, but we do guarantee the consistency of your filesystem. It is true that disks themselves have caches, and I'm not sure what guarantees the hardware makes about those, but I believe that the idea is that if the os block driver asks for a write of a single block, the drive is pretty much guranteed to have enough power to finish that write. I'm not totally sure on this, though. Of course, as stated in the article, we in the free BSD world have been enjoying soft updates for a long time now, so this idea isn't all that revolutionary.