Siebel Installation Guide for Microsoft Windows: Servers, Mobile Web Clients, Tools > Configuring the RDBMS > Configuring MS SQL Server for Siebel Applications >

Guidelines for Allocating MS SQL Server Database Log Space

You must place your log on a disk large enough to hold the log as it expands. Monitor the disk regularly for its level of utilization. Very large transactions may, for example, require at least 1 GB.