When the server zeros a page, UNIX allocates disk space for that page of the file. Therefore, all space specified in create database is initialized. A dump only contains images of allocated pages. After the dump is loaded, the server initializes all unallocated pages, including the additional pages if the dump was loaded into a database that is larger than the original database. This lazy allocation scheme can be confusing.
Allocation only occurs when a program stores information in a particular location of the file.
Initialization normally occurs when tempdb is first created and altered. However, under some circumstances, the tempdb device pages may not be allocated. This is most commonly done if the device is created on a Solaris tmpfs device, but may be done as a remedy for an accidental deletion of the device. Creating a Disk File Creating a disk file with disk init does not allocate all of the disk space needed to hold the file, only enough disk space to hold the information currently in the file. However, UNIX allocates only two blocks on the disk to mark the beginning and end of the file.