Hello,
Could please let us know the entire SEP 12.1 version?
Is it SEP 12.1 RU1? This was a known issue in this version where the Symantec Endpoint Protection 12.1 RU1 Small Business Edition database transaction log becomes excessively large. This file may grow to 20GB or more.
SEP SBE is designed to perform this database maintenance as well, but on a fixed schedule that is not configurable within the user interface. In SEP SBE 12.1 RU1, the transaction log does not seem to reduce in size. In SEP SBE, there is also no Truncate Transaction Log Now button.
Since in your case, you may try the steps provided in the Article below:
Symantec Endpoint Protection Manager (SEPM) database transaction log (sem5.log) consumes excessive hard drive space in SEP SBE 12.1 RU1
http://www.symantec.com/docs/TECH178718
Shrink the Symantec Endpoint Protection Manager (SEPM) 12.1 embedded database
http://www.symantec.com/docs/TECH185177
Hope that helps!!