uses ordinary files and directories to store revisions of ZODB objects; one
file per revision per object.
The following features differentiate DirectoryStorage from other storages:
* A very simple file format; one file per revision per object. Your data is
not locked away inside an unfamiliar, opaque database.
* Designed for disaster-preparedness. Restore service after a disaster faster
and with greater confidence.
* Storage Replication. Efficiently and robustly keep an online backup copy of
your storage up to date with the latest changes from the master.
* Designed for fault tolerance. Any bugs (in DirectoryStorage, or elsewhere)
are less likely to irretrievably destroy your data.
* Many more.
