Update index.md

Author: paigehargrave

storage/storagedriver/index.md

@@ -16,7 +16,10 @@ your applications and avoid performance problems along the way.
 
 Storage drivers allow you to create data in the writable layer of your container.
 The files won't be persisted after the container is deleted, and both read and
-write speeds are low.
+write speeds are lower than native file system performance. 
+
+ > **Note**: Operations that are known to be problematic include write-intensive database storage, 
+particularly when pre-existing data exists in the write-only layer. More details are provided in this document.
 
 [Learn how to use volumes](../volumes.md) to persist data and improve performance.