While attending a class on SQL Server, I was introduced to a paper from Microsoft Research (authors are Russell Sears, Catharine Van Ingen and Jim Gray) that discusses whether to store large objects in a filesystem or in a database, depending on the size of the object in question.

White Paper Title: To BLOB or Not To BLOB: Large Object Storage in a Database or a Filesystem

Abstract: Application designers often face the question of whether to store large objects in a filesystem or in a database. Often this decision is made for application design simplicity. Sometimes, performance measurements are also used. This paper looks at the question of fragmentation – one of the operational issues that can affect the performance and/or manageability of the system as deployed long term. As expected from the common wisdom, objects smaller than 256K are best stored in a database while objects larger than 1M are best stored in the filesystem. Between 256K and 1M, the read:write ratio and rate of object overwrite or replacement are important factors. We used the notion of “storage age” or number of object overwrites as way of normalizing wall clock time. Storage age allows our results or similar such results to be applied across a number of read:write ratios and object replacement rates.
 
URL: http://research.microsoft.com/apps/pubs/default.aspx?id=64525