This option is used to specify the expansion limit in megabytes of the volume being created. Values are automatically rounded up to the next power of 2 (100 becomes 128). Specifying 0 prevents the volume from being expanded in the future.
The default value is the same size as the create size rounded up to the next power of 2. For example, a 70 MB volume by default would be expandable to 128MB. A 60 MB volume could be expanded to 64 MB. An exception to this rule is that if /SILENT is included on the command line and /EXPANDABLETO is not, then the volume cannot be resized. Hence, it is usually a good idea to include this option when /SILENT is used.
/EXPANDABLETO = NNN