Can I create a second filestream container on an existing SQL Server 2008 database without going offline? Our production DB is using the FILESTREAM option for our sharepoint environment. The volume where the files are residing is getting full and I am planning to add another volume to ease space issues. Is the solution as simple as creating another filestream container and adding this container on the existing filestream filegroup? Would SQLServer take care of balancing among the two volumes?
Unfortunately no, not in SQL Server 2008.

According to FILESTREAM Overview - multiple containers can be added to a single FILESTREAM Filegroup but only as of SQL 2012.