diff --git a/doc/soju.1.scd b/doc/soju.1.scd
index df33be4..2eee35f 100644
--- a/doc/soju.1.scd
+++ b/doc/soju.1.scd
@@ -134,10 +134,14 @@ The following directives are supported:
 
 	Supported drivers:
 
-	- _memory_ stores messages in memory.
+	- _memory_ stores messages in memory. For each channel/user, only the
+	  latest 4K messages are kept in memory, older messages are discarded.
 	- _fs_ stores messages on disk, in the same format as ZNC. _source_ is
-	  required and is the root directory path for the database.
-	- _db_ stores messages in the database.
+	  required and is the root directory path for the database. This on-disk
+	  format is lossy: some IRCv3 messages (e.g. TAGMSG) and all message tags
+	  are discarded.
+	- _db_ stores messages in the database. A full-text search index is used to
+	  speed up search queries.
 
 	(_log_ is a deprecated alias for this directive.)