add note about storage verification

DOCUMENTATION.md

@@ -1058,6 +1058,8 @@ Default: `False`
 
 Note: check used filesystem mtime precision before enabling
 
+Note: conversion is done on access, bulk conversion can be done offline using storage verification option `radicale --verify-storage`
+
 ##### folder_umask
 
 Use configured umask for folder creation (not applicable for OS Windows)

config

@@ -157,6 +157,7 @@
 
 # Use last modifiction time (nanoseconds) and size (bytes) for 'item' cache instead of SHA256 (improves speed)
 # Note: check used filesystem mtime precision before enabling
+# Note: conversion is done on access, bulk conversion can be done offline using storage verification option: radicale --verify-storage
 #use_mtime_and_size_for_item_cache=False
 
 # Use configured umask for folder creation (not applicable for OS Windows)