EMCS-4449: adds preallocDataFiles setting to ref

Author: schmalliso

source/includes/options-conf.yaml

@@ -1035,4 +1035,18 @@ inherit:
   name: chunkSize
   program: mongos
   file: options-mongos.yaml
+---
+program: conf
+name: storage.preallocDataFiles
+type: boolean
+default: true
+directive: setting
+replacement:
+  program: ":program:`mongod`"
+description: |
+  Enables or disables data file preallocation. 
+post: |
+  Do **not** disable data file preallocation in production systems. Only
+  use this option for testing and with small data sets where you
+  frequently drop databases.
 ...