W. Curtis Preston recently authored an article on Searchstorage.com.au explaining global deduplication. This is an important topic which frequently causes confusion. Curtis does a good job explaining the technology and what it means to end users and I recommend the article.
A quick summary is that global deduplication means that a common deduplication repository is shared by multiple nodes in a system. In these environments, a customer can backup their data to any node on a system and it will be deduplicated against related data. This provides improved ease of use and scalability.
The alternative is the multiple unit approach which requires separate systems and deduplication repositories. In this model, shifting a backup job to a different appliance results in minimal deduplication benefit since each system maintains a separate and independent deduplication repository.
Today’s enterprise environments are changing rapidly. End users must plan for the future and global deduplication provides the flexibility they need to meet their business requirements. A single system design works well in smaller SME/SMB environments, but rapidly becomes unmanageable as environments grow.