SAS does not pre-allocate storage when SAS initializes or when performing writes to a file. For example, in extent-based file systems. When SAS creates a file it allocates a small amount of storage, but as the file grows during a SAS task, SAS requests extents for the amount of storage needed.
NOTE: File extension is limited to the amount of physical space available within a file system. SAS datasets and individual partitions within an SPDS table do not span file systems.