SharePoint 2010:Remote BLOB Cache

By default, a SharePoint farm uses content databases on SQL Server as its only data source. Farm content generally includes documents and pictures, which can each be on the order of several megabytes in size. Files and other unstructured data have historically been stored as binary large objects (BLOBs) within the database.

While there have been many improvements in the way that BLOBs are handled within a SQL Server database3, there are limitations. The VARBINARY(MAX) data type is used for native BLOB storage, and can accommodate files up to two gigabytes (2147483648 bytes) in size. In rare circumstances, this may not be adequate for all of the files that will be stored in the farm. Also, the performance of writing BLOBs to and retrieving BLOBs from the database is generally not as good as the performance offered by file systems, which can degrade users’ perception of a SharePoint solution.

Remote BLOB Storage (RBS) feature pack is available for SQL Server 2008 and SQL Server 2008 R2; it provides libraries and APIs that allow SQL Server to interact with BLOBs stored outside of the database. SQL Server 2008 and SQL Server 2008 R2 provide a data type called FILESTREAM that allows BLOBs to be stored within an NTFS volume, but managed by the database. This feature cannot be directly used by SharePoint4, but there is an RBS provider for FILESTREAM that can be used with local SharePoint databases (such as those often employed by SharePoint Foundation 2010); this local database requirement makes the FILESTREAM provider for RBS unsuitable for most farm-based architectures. For farm deployments with separate database servers, RBS providers other than FILESTREAM may still be used.

For example, a provider for a dedicated external store, such as an EMC2 Centerra system, that makes use of the SQL Server RBS API calls may be employed. These RBS providers allow third-party products to leverage RBS to store and retrieve files that reside outside of the database. Using Remote BLOB Storage requires configuration of both SQL Server 2008 (or SQL Server 2008 R2) and SharePoint Server 2010. These systems are expected to offer higher performance for reading and writing large files, but will generally require special attention when administering sites or performing backup/restore operations.