rslg/write_sync_disk is a SAP Parameter attribute which is used to control synchronous write to disk of syslog messages 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 .
Force synchronous write to disk if set to one. Allows operating system's
cache to be used when set to zero.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.