The Storage Admission Tier (SAT)
The tiered storage architecture provides the basic framework for the application of intelligence to storage management. It provides a solid infrastructure on which data management policies can be enforced. However, the manner in which they are enforced will ultimately influence the efficiency of the storage architecture. In most storage deployments today, a tiered architecture is flat when it comes to the layer of intelligence. Each tier has limited capability to operate intelligently on the data, and the farther a tier from the actual application layer, the less information is available at that tier to operate intelligently on the files and control management of that data. A good example is HSM or ILM software which typically resides orthogonally to the tiered model as shown in the diagram below.
The ILM software for example, resides on externally induced intelligence to migrate files from one tier to the next, leaving meta data (such as shortcuts, or vendor specific stub files) on the primary as they move files to secondary tiers so as to control the storage consumed on the primary and therefore providing cost savings. While such techniques genuinely contribute toward cost savings, they have implementation overheads and have their own quirks (such as management of the stub files themselves). Furthermore, as application infrastructure changes, for example with the addition of new application services, changes are required on the ILM strategies as to the location of the data (allocated shares or volumes for that application) and policies for its migration and file management. Also, when storage operations such as backup restores are performed (for example, during disaster recovery), the HSM or ILM software will need to get involved.
Given the coupling (chaining) nature of the storage networking protocols such as CIFS, NFS or iSCSI, one can see that the introduction of a tier dedicated to storage management is an architecturally correct approach to managing information stored into the storage network. Such a tier, known as the storage admission tier precedes the tier one storage services, such as those offered by a NAS filer.
Read more about this topic: File Area Network
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