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The Domino Attachment and Object Service (DAOS) is a new feature introduced in Domino 8.5. DAOS is a mechanism which shares identical attachments between databases on the same Domino server. When configured, separate and complete attachments are no longer stored within a database, rather a single copy of an attachment is stored on the file system with documents referring to them on the disk. DAOS is implemented such that the creation and retrieval of attachments is transparent to all transactions, including all user functions. The benefit of DAOS is file size reduction. Any Domino database is eligible for participation in DAOS.
This article discusses when to deploy it in your environment.
For information on DAOS architecture, see
IBM Lotus Domino going green: The new Lotus Domino attachment and object service
The following flowchart provides the guideline on when to deploy DAOS.

There are various technotes and articles available about DAOS including how to configure it and how to estimate its impact.
How can you be sure if every server needs this? Should it be enabled on Traveler? No! Should it be enabled on company cluster servers hosting several hundreds of gigabytes of data? Definitely Yes!
When DAOS is used on a server, additional tasks are running on a server. DAOS also requires changes in your backup procedure; because in addition to NSF files the .NLO files need to be backed up.
DAOS is introduced in 8.5.0, but to be on a safe side, before implementing DAOS, you should make sure you are on the recommended version of Domino for optimal DAOS operation.
You also need to disable "Shared Mail" if it is used. Use this above flowchart as a guideline. Do not run DAOS Estimator during working hours. Do this after working hours.
You can also use DDM(Domino Domain Monitoring) to monitor DAOS.
The following references illustrate the configuration and administration requirements for DAOS: