Query regarding working of SEPM Console

Sir

   My sem5.log has occupied 15 GB. and Backup file 2GB.As my Disk space got full ,I removed both  files to a different machine.and started SEPM.It was not coming up & I found that Synnamtec Embedded Database has stopped.After copying again SEM5.log it started working.  Is the working of SEPM dependent on this log?Is this log gets updated automatically?

 In my console,already Truncate transaction of logs every 4 hours & Rebuiding of Indexes weekly givenPlease guide me.