On Sat, Jun 11, 2011 at 12:58:26PM +0300, Amir G. wrote: > I meant _readonly_ snapshots of a _writable_ _external_ origin, > which is what ext4 snapshots provides. > All snapshots are chained on a list that points to the origin and > only the latest (active) snapshot metadata get updated on origin writes. > When older snapshots lookup return -ENODATA, you go up the list > to the newer snapshot and up to the origin. > > Those _incremental_ snapshots cannot be _writable_, because older > snapshots may implicitly share blocks with newer snapshots, but it should > be possible to make _writable_ clones of these snapshots. > Not sure what the implications are for deleting snapshots, because I am > not familiar with all the implementation details of multisnap. I deliberately ruled out chaining schemes like this because I want to support large numbers of snapshots. I believe Daniel Phillips described a chaining scheme a while ago, and someone else implemented it last year. From a cursory glance through the code they posted on dm-devel, it appeared to need a large in memory hash table to cache all those chained lookups. - Joe -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
