To create a database on a database device and allocate a certain amount of space to it, Adaptive Server first makes an entry for the new database in sysdatabases. Then, it checks master..sysdevices to make sure that the device names specified in create database actually exist and are database devices. If you did not specify database devices, or if you used the default option, Adaptive Server checks master..sysdevices and master..sysusages for free space on all devices that can be used for default storage. It performs this check in alphabetical order by device name.
The storage space from which Adaptive Server gathers the specified amount of storage need not be contiguous. The database storage space can even be drawn from more than one database device. A database is treated as a logical unit, even if it is stored on more than one database device.
Each piece of storage for a database must be at least one allocation unit. The first page of each allocation unit is the allocation page. It does not contain database rows like the other pages, but contains an array that shows how the rest of the pages are used.
