Estimating Disk Usage Space

For Campus Solutions, PeopleSoft has done some preliminary research on the sizing of a production system. PeopleSoft realizes that the theoretical amount of disk space required by an application is different than the actual amount of disk space required by a database. The difference is due to comparing bytes with database blocks. For instance, if a particular table's average row length is 25 bytes and there are 1,000 rows in the table, theoretically the required amount of space is 25,000. However, if the database block size is 4K (4096), the number of database blocks required to hold the data is seven blocks or 28,673. Therefore, the actual amount of disk space required is greater than the theoretical. With this in mind and realizing that each installation may require a different block size, PeopleSoft states the size in theoretical terms.

For 1,000 student prospects, the amount of space needed for tables and indexes would be 40 megabytes (MB).

For enrollment, PeopleSoft needs to work with a specific, albeit theoretical, scenario. PeopleSoft's scenario was to enroll 1,000 undergraduate students over three terms into four classes per term. In the first term, there are no prerequisites to enroll in any of classes; the second term has one prerequisite for each of the classes; the third term has two prerequisites for each of the classes. During enrollment, the students have no time conflicts and there is no lack of facilities (rooms or seats). The amount of disk space excludes description information stored in long text fields. For 1,000 student enrollments, the amount of space needed for tables and indexes would be 20 MB.