what is single instance storage
Single Instance Storage. The Single Instance Storage (SIS) feature reduces the amount of space that is used to store data on a volume. SIS does this by replacing duplicate files with logical links that point to a single copy of the file in the SIS Common Store, which is a hidden folder that is located in the root directory of the volume.
Single-Instance Store and SIS Backup. Single-instance store, or SIS, is an architecture designed to maintain duplicate files with a minimum of disk, cache, and backup media overhead. Single-instance store backup, or SIS backup, is an API that backup applications call to access the SIS architecture. For more information, see the following topics: