rspo/global_shm/server_list is a SAP Parameter attribute which is used to control Startup cache size for spool server cache 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 .
Every instance has a list available servers with spool-relevant
attributes. This server list includes both active and logical servers,
as well as other servers defined for output devices. This list is
dynamically expanded if the startup size is too small.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.