On Thu, Feb 14, 2019 at 9:00 PM Remi Gauvin <r...@georgianit.com> wrote: > > > > It doesn't work this way. The snapshots a and b are not based on the > > same underlying subvolume. The gist is that you would keep changing A, > > and take additional snapshots of A, such as a.1 a.2 a.3, and you can > > do incremental send with 'btrfs send -p a.1 a.2' which describes the > > difference between those two snapshots of A at their respective > > moments in time. You could also do 'btrfs send -p a.2 a.3' or even > > 'btrfs send -p a.1 a.3' > > > > But as there's no relationship between > > snapshots a and b, I consider > > it a bug/missing error handling feature, that btrfs send doesn't fail > > in this case. By using -p you're claiming there is a parent-child > > relationship between a and b, but there plainly isn't. > > They kind of are related though, since the two snapshots reference the > same data blocks, and you can see it work in the first example with the > 40MB of random data.
Is it more of a case for clone, -c option? I don't ever use it, and the man page could use a couple examples to make it more clear what it can do. And it makes sense this option could be more tolerant, less error checking, than -p. But from man page and in particular the wiki, it's clear to me that the two snapshots following -p option, need to each be derived from one subvolume. I actually don't like the "parent - child" metaphor because really the parent is the original source rw subvolume, and its two children snapshots are the ones used with -p. The first is an older sibling, the second a younger sibling. And that metaphor fails too because you'd expect the second sibling to have more information which plainly is not the case with actual siblings. :P > The out file is only 773 bytes. However, if you repeat all those same > steps, but replace the dd with: > wget -O A/dir/server.jar > https://launcher.mojang.com/v1/objects/20c069d373e77265aaeeedb733f7051e294325a3/server.jar > > The resulting out file is 34MB. Well I'd say maybe use -vvv and --no-data instead of -f and see what it's doing. It sounds like the former has no payload, just difference information, and the latter has a payload. I don't know why. -- Chris Murphy
