preallocation

Prespecifying space for a file so that disk blocks will physically be part of a file before they are needed. Enabling an application to preallocate space for a file guarantees that a specified amount of space will be available for that file, even if the file system is otherwise out of space.

A method of allowing an application to guarantee that a specified amount of space is available for a file, even if the file system is otherwise out of space.