depends what you mean by "extra". if that means "outside 9vx", then yes; if it means "besides what 9vx uses by default", no.
yesterday(1) relies on having dump-style snapshots. 9vx, as shipped, gets its root file system from #Z, which doesn't have snapshots. erik offered some suggestions for hosting various bits of things outside 9vx and connecting to that in order to get the dumps. those options are valid, but you can just as well host the entire thing within 9vx. it's not the default configuration, but i believe instructions are out there (9fans or the wiki). using fossil for your root, instead of #Z, will obviously cost you the benefits of #Z - namely, the pass-through transparency. if your primary interest is for replica/*, though, you might consider the direction i've been headed: root from fossil, but import $home or /usr from #Z.
