Single Instance Storage
From Wikipedia, the free encyclopedia
Single instance storage is a system's ability to keep one copy of content that multiple users or computers share. It is a means to eliminate data duplication and to increase efficiency, SIS is frequently implemented in e-mail server products and data backup solutions.
In the case of an e-mail server, single-instance storage would mean that a single copy of a message is held within its database whilst individual mailboxes access the content through a reference pointer. However there is a common misconception that the primary benefit of single instance storage is a reduction in disk space requirements. The truth is that its primary benefit is to greatly enhance delivery efficiency of messages sent to large distribution lists. In a mail server scenario disk space savings from single instance storage are transient and drop off very quickly over time.
When used in conjunction with a backup solution, single instance storage can reduce the quantity of archive media required since it avoids storing duplicate copies of the same file. Often identical files are installed on multiple computers, for example operating system files. With solutions that use single instance storage, only one copy of a file is written to the backup media therefore reducing space.
Single Instance Storage has been a feature of Microsoft Exchange Server since version 4.0 and is also present in Microsoft's Windows Home Server. It is protected by several patent applications, including United States Patent numbers 6389433 and 6477544.
