[ Thanks to Flavio
Villanustre for this link. ]
“Many times, you need to know how a certain filesystem looked
like at some point in time, and you want to be able to roll back
changes that happened to it after that point. While there are
multiple solutions to achieve this goal, certainly one of them is
to use filesystem snapshots.“Unionfs lets you recursively merge many underlying directories
(branches) into a single and consistent view. It utilizes a fan-out
structure and has a relatively low overhead (under about 12% for 4
branches)…”