diff --git a/Master-Server-API.md b/Master-Server-API.md
index df122f4..2288984 100644
--- a/Master-Server-API.md
+++ b/Master-Server-API.md
@@ -30,7 +30,7 @@ curl "http://localhost:9333/dir/assign?dataCenter=dc1"
 | preallocate | If no matching volumes, pre-allocate this number of bytes on disk for new volumes.  | master preallocateSize |
 | memoryMapMaxSizeMb | Only implemented for windows. Use memory mapped files with specified size for new volumes.  | 0 |
 | writableVolumeCount | If no matching volumes, create specified number of new volumes.  | master preallocateSize |
-
+| disk | If you have disks labelled, this must be supplied to specify the disk type to allocate on. | empty |