While the amount can, in generic terms, be the database size, it could also be the size of an interface file that is the subject of volume testing. For example, if one wants to volume test an application with a specific database size, the database will be expanded to that size and the application's performance will then be tested on it. Another example could be when there is a requirement for the application to interact with an interface file (could be any file such as .dat, .xml); this interaction could be reading and/or writing on to/from the file.
This concept refers to the quantity that can encompass database size, but it also pertains to the size of a specific interface file that is subject to thorough testing. For example, if someone wants to test an application's performance with a predetermined database size, the database will be enlarged to that size and then its functionality will be examined on it. Alternatively, when there is a requirement for the application to engage with an interface file (which could be any type of file such as .dat or .xml), this interaction may involve reading from and/or writing to the file.