On Fri, Sep 10, 2010 at 08:22:14AM -0500, Anthony Liguori wrote: > fsck will always be fast on qed because the metadata is small. For a > 1PB image, there's 128MB worth of L2s if it's fully allocated (keeping > in mind, that once you're fully allocated, you'll never fsck again). If > you've got 1PB worth of storage, I'm fairly sure you're going to be able > to do 128MB of reads in a short period of time. Even if it's a few > seconds, it only occurs on power failure so it's pretty reasonable.
I don't think it is. Even if the metadata is small it can still be spread all over the disks and seek latencies might kill you. I think if we want to make qed future proof it needs to provide transactional integrity for metadata updates, just like a journaling filesystem. Given that small amount of metadata and less different kinds it will still be a lot simpler than a full filesystem of course.
