I had to solve this problem at my last job and we had vendors let us know how companies like Apple, Sony, Disney, EA etc have solved it. Basically there are two ways to do it. (1) Store it on some "filesystem". In quotes because how you do it can vary wildly e.g. S3, GlusterFS, Standard directories using DRBD for HA. (2) Take the blob, slice it into pieces, hash it and spread it across a sharded database.

Generally it seems to be that if you have lots of unique large files then use filesystem. But if you have files which are likely to have duplicates then use a database. So a file storage locker may use (1) but a service like iTunes Match would use (2). And IIRC Apple in fact does store at least uploaded music files in Cassandra.

Usually storing in filesystem with a reference in database seems to work best. Much easier for database management and backup, and file management as well.

The OP doesn't appear to have hear of SQL Server FileStream or FileTables, which handle this abstraction for you: http://msdn.microsoft.com/en-us/library/ff929144.aspx

On pgsql, the blob type. It stores the object out of the row store, but still in the database.

commonly, s3 or zfs nas for storage and pg for metadata