-this may lead to transient errors reported by code that assumes that the files
-are already existing. When disabled (the default) files are created
-synchronously, blocking for a short while, while the file is being written.
+since the purpose of creating the files asynchronously is I<not> to block until
+the file is available, values before the file is available will be discarded.
+When disabled (the default) files are created synchronously, blocking for a
+short while, while the file is being written.