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Single Instance Storage (SIS) is a feature that enables the storage of a single copy of any archived message attachment. A hash value that uniquely represents the attachment file is stored and used to later retrieve the file from the archive. SIS is especially useful in email environments where messages with attachments are forwarded to many users. In non-SIS archiving, each copy of the forwarded message attachment is stored, even though the attachments are identical. With SIS, if an attachment is already archived, subsequent archives of the same message attachment point to the existing archived attachment.

The Storage Abstraction Interface (SAI) is the component of Netmail Archive that designates hash values to message attachments and determines if an attachment has already been stored. The SAI interacts with multiple storage devices, allowing implementation of SIS for all your storage devices.

How SIS functions in Netmail Archive:

1. A message with an attachment is archived by the Netmail Archive server and is sent to the SAI for storage assignment.

2. The SAI generates a hash value for the attachment and performs a search against the Dynamic Data Store Share. The hash value of an attachment is used in the folder name of that attachment to uniquely identify it.

Note: Netmail Archive contains two types of data stores: Dynamic Data Store and Static Data Store. You can configure your data stores on the Storage tab of the Clusters object. For more information about configuring your data stores, see “Specifying Locations”.

  • Dynamic Data Store: Audit files and indexes are stored in the Dynamic Data Store. The Dynamic Data Store also contains the stubs of all attachments archived in the system. It is located on the file system of your choice.
  • Static Data Store: Messages and attachments are stored in the Static Data Store, which is located on the storage device or file system of your choice.

3. If the hash exists, this means an instance of the attachment has already been stored. The SAI updates the message only and commits it to the Static Data Store. The audit files and index are updated on the Dynamic Data Store to point to the existing stored attachment.

4. If the hash does not exist, the SAI commits the attachment to the Static Data Store and creates a stub of the attachment on the Dynamic Data Store. The stub is used to resolve the attachment during lookups. The SAI also updates the message and commits it to the Static Data Store, and updates the audit files on the Dynamic Data Store and updates the index entry.

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