Since you mention using vac for storage, I assume you're using venti directly, not via fossil, in which case the '9fs dump' suggestion will do nothing for you.
I don't believe there is anything in Plan 9 that does what you want (certainly the BUGS section in venti(1) implies not), but you might look at vcat in p9p. It's not quite there - it seems to demand that you're working with only a single file, rather than directory trees (possibly containing only a single file) as vac creates - but does the redirection and may be close to what you want. Anthony
