The latest update to Windows Storage Server adds Single Instance Storage (SIS), a feature that Microsoft claims can reduce storage demands up to 70 percent.
SIS has been available for some time in certain applications software, including archiving programs for applications like Microsoft Exchange. The feature has also been available on versions of Microsoft Server 2003 with Remote Installation Services.
How much space SIS will save on a Storage Server very much depends on the nature of the data being saved. The more duplication, the more savings. With e-mail, where the same message and attachments are sent to a lot of people, the 70 percent savings that Microsoft quotes is fairly common. . .perhaps even conservative. But the opportunity for savings decreases in environments with less redundancy.
In Microsoft's version of SIS, Storage Server scans all the files on the server and eliminates duplicates. Duplicated files are saved to a separate Common Store folder hidden in the server's root directory, and each instance is replaced by a link. The process is invisible to the users, since the link will be followed to the file automatically. When users create a unique copy of the file, the original is copied back to the user's directory from the Common Store and the changes are applied to the new copy.
To further conserve storage space, Microsoft has provided an SIS API. This allows makers of backup software to use the single instance files instead of automatically following the links and backing up multiple copies of the file.
Microsoft has outlined the features of Storage Server R2 in a white paper.
About the author: Rick Cook specializes in writing about issues related to storage and storage management.
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