SCCM 2012 R2 default installation is Report Server database log file grow by 10% by day. I was stucked- the free space of hard drive was mistically eaten, early I thought it is windows patches but no, it was Report Server log files, default installation allows to grow in size up to 2 terrabytes, it remembers all reports since born. First thing to do is swith beckup from full to simple, otherwise you can' t shrink log files. As you cannotice log file enlarges in 60 GB while Report database is some 45 MB. I was stucked for few days so I started to check space in folders. To do that you need to log in with user who actually installed SCCM, domain admin rights is not enough.