rsau/max_diskspace/per_file is a SAP Parameter attribute which is used to control Maximum size of one single security audit file information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
The parameter specifies the maximum size of a security audit file. This
means the file size can be adjusted to the requirements of any available
archiving software. For example, the size can be restricted to 650
megabytes in order to be able to archive on normal CDs. If this size is
reached, then a new audit file is started. The counter in the file name
is then increased by one for the new file.
Only when this parameter is greater than zero can more than one audit
file be created each day. In this case the file name of the audit failes
also changes (see parameter FN_AUDIT).
See SAP Parameter Documentation for full SAP documentation for this profile parameter.