The Register published an article describing the removal of Single Instance Storage (SIS) from the Exchange Server 2010 database engine.  The comments on the article were largely critical of the change, declaring it a backward step in Exchange storage efficiency.

Before I discuss this further it helps to go back in time a little and understand what SIS is and how it came to be a part of Exchange Server.

Exchange Server Single Instance Storage

The essence of SIS is the storage of a single copy of data that is shared among different users or computers.  In the case of Exchange Server this meant a single copy of an email or file attachment is kept in the mailbox database, and then any user who received that item accesses it via a pointer to that one single instance of the item.

SIS was introduced in the Exchange Server product line in version 4.0 back in 1996.  Back then disk storage was very expensive compared to today’s prices.  Disks were much larger in physical size, smaller in capacity, and slower in performance.  Under those conditions SIS made a lot of sense to reduce the overall size of mailbox databases.

SIS remained a part of the Exchange database engine right up to Exchange Server 2007.  However in this time the price of disk storage has greatly reduced.  The database engine itself had also been improved and between Exchange Server 2003 and 2007 saw as much as a 70% decrease in IOPS (Inputs/Outputs per Second) requirements, meaning more users and larger databases could be stored on fewer disks. Continue reading Does the Removal of Single Instance Storage Mean Less Efficient Exchange Servers?