On Fri, 15 Aug 2008 01:43:55 -0700 Daniel Phillips <phillips@xxxxxxxxx> wrote: > > A daemon program requests delta from the > > kernel, and sends it to another daemon program on the remote > > server. The daemon on the remote server asks the kernel to apply > > delta. > > The downstream server just writes the delta to the origin, there is no > need to ask the kernel to do this. > > > The advantage of this approach, the above replication program can work > > with any snapshot implementation, which could live in dm or file > > systems like btrfs. File systems could implement the snapshot features > > more efficiently than dm. > > When you replicate a volume you can just send a list of changed blocks > as ddsnap does. This is not the case with a filesystem delta, which > has to send the changed blocks of each filesystem object logically, > along with relevant metadata such as changed permissions, ownership, > file sizes etc. What I think about is... User-space replication programs don't know anything about delta. Delta might be a list of changed blocks, or something more complicated. So the downstream server can't simply write the delta to the origin. It always asks the kernel. User-space replication programs don't care about the format of delta. A file system can give user-space programs whatever as delta. All a file system needs to do is applying the delta that it gave to user space. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
