I know that is my fault, the warning was there several month, but today TeamCity collapsed with unexpected error. The internal database exceeds 2GB and refuse any inserts.
So I followed the instraction for migration to external database (they are excellent by the way) but as migrateDB.cmd is logging its work to the old database so the full migration failed. Also simple db backup failed. I had to migrate from an older backup. Could it be possible to add --no-log option to the maintainDB batch, or don't fail whole process on failed logging?