doc: rewrite decision.
# Multiple File Backends
+Usually, a backend refers to exactly one file per namespace.
+This file can be returned using `kdb file`.
+
## Problem
-- For XDG in the `system` namespace may contain several files (XDG_CONFIG_DIRS)
-- Unreachable sources (e.g. `curl`) need some fallback
-- As fallback source if some data cannot be stored in some format
+In some situations a single mountpoint refers to more than one file per namespace:
+
+- For XDG in the `system` namespace may contain several files (XDG_CONFIG_DIRS).
+- A fallback file if some data cannot be stored in some format (Idea from @kodebach:
+ writing the same content to several files, merging when reading)
## Constraints
## Decision
-Multiple File Backends are not supported as they:
+Multiple File Backends are not supported for now in the case of writing files.
+Read-only fallbacks should not be a problem.
-- make it impossible for admins to modify content of all files
-- do not work atomically (a journal would be needed)
-- do not work together with mmap
+## Rationale
-Instead all but the first of the files in `XDG_CONFIG_DIRS` are ignored
-and unreachable sources yield an error.
+Writeable multiple file backends would:
-## Rationale
+- make it impossible for admins to modify content of all files using Elektra
+- do not work atomically (a journal would be needed)
+- do not work together with mmap (as it only checks one file for cache misses)
## Implications
