On Thu, Jun 04, 2009 at 10:49:19AM +0200, Thomas Glanzmann wrote: > Hello Chris, > > > > My question is now, how often can a block in btrfs be refferenced? > > > The exact answer depends on if we are referencing it from a single > > file or from multiple files. But either way it is roughly 2^32. > > could you please explain to me what underlying datastructure is used to > monitor if the block is still referenced or already free? Is a counter > used, bitmap (but that can't be if is 2^32) or some sort of list? I > assume that a counter is used. If this is the case, I assume when a > snapshot for example is deleted the reference counter of every block > that was referenced in the snapshot will be decremented by one. Is this > correct or am I missing something here?
It is a counter and a back reference. With Yan Zheng's new format work, the limit is not 2^64. When a snapshot is deleted, the btree is walked to efficiently drop the references on the blocks it referenced. >From a dedup point of view, we'll want the dedup file to hold a reference on the file extents. The kernel ioctl side of things will take care of that part. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
