All valid front end configurations can be combined with all valid back end
configurations.

Front end configuration
=======================

No support or no blob support configured
----------------------------------------

- andere einstellungen sind irrelevant, sollten auf `unconfigured` stehen

Blobs via ZEO protocol
----------------------

ClientStorage options:

- blob-dir configured to a seperate physical directory on each client

- shared-blob-dir set to `false`

Blobs via file system shared with ZEORaid
-----------------------------------------

- blob-dir configured to a directory shared between the zeo clients and the
  RAIDStorage's blob-directory (read/write for all participants)

- shared-blob-dir set to `true`


Back end configuration
======================

RAIDStorage and back-ends with a single shared file system
----------------------------------------------------------

- blob-dir configured to a directory shared between raidstorage,
  clientstorages and back-end servers (read/write for all participants)

- shared-blob-dir for raidstorage and clientstorages set to `true`


RAIDStorage via storage API and back-ends with individual shared file systems
-----------------------------------------------------------------------------

- RAIDStorage and ClientStorages have separate blob directories

- each ClientStorage shares its blob directory with its ZEO server

- RAIDStorage has shared-blob-dir set to false

- ClientStorages have shared-blob-dir set to true


RAIDStorage via storage API and back end via ZEO protocol
---------------------------------------------------------

- blob-dir configured to separate directories in raidstorage, clientstorages
  and back-end servers

- shared-blob-dir for raidstorage and clientstorages set to `false`


Invalid combinations: mixture of shared and non-shared
------------------------------------------------------

- The raidstorage having a shared directory with the zeo clients but the zeo
  clients not sharing with the back end servers is unsupported.

- The raidstorage using the storage API against zeo clients which share their
  blob directory is unsupported.

Warning: ZEORaid can not automatically detect those invalid combinations and
might destroy data if those are configured.

