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Cisco's Unified Storage Fabric

Cisco has announced a product to move services that normally run on storage arrays and tape libraries into their MDS9500 storage director. The Storage Services Node-16 (SSN-16) is a blade for the MDS9500 that brings in services such as encryption, Fiber Channel over IP and migration into the MDS switch fabric. It allows those features to be used within a heterogeneous storage architecture. The SSN-16 is available now through resellers.

Cisco states the SSN-16 and software make a services-oriented SAN where services reside in the SAN fabric rather than on the end devices like storage arrays and tape drives. The strategy is similar to Cisco's move in the 90's to build smart networks using the Catalyst platform. "We've seen this pendulum swing before. Storage administrators love services in the fabric because they can better support a heterogeneous environment," Network Computing blogger and Chief Scientist Howard Marks said.

The smart network/dumb network argument highlights a philosophical divide in architecture. Proponents of the dumb network view the networks as pipes that are responsible for delivering packets from point-to-point with as little interference as possible. It tends to make the network simpler to build, manage and troubleshoot. You can add any interoperable network device like a firewall, load balancer or router to the network and it works. Smart networks perform more processing in the switches and routers such as managing quality of service, grooming traffic and embedding security and performance features in the network hardware. Smart networks often are more feature rich, but building the network and troubleshooting problems are more difficult because there are more processes interacting with traffic. Additionally, smart networks generally mean you are more closely tied to a single vendor.

The case Cisco makes is that adding features into the SAN fabric offers a more dynamic storage network and since the processing can occur on the backplane versus physical ports and we would generally agree. Adding appliances for encryption, MAN/WAN backup and replication and other services complicates physical installation and the data paths. That also means you can only use Cisco features on the SSN-16. However, being tied to a single vendor is less of an issue in storage where approved equipment lists and vendors are the norm rather than the exception--the opposite of what we have in Ethernet networking today.

The SSN-16 has four processing engines which individually can run a separate process such as encryption, migration, IO acceleration and other services. The SSN-16 replaces up to four Multi-Service Modules (MSM 18/4) with a single module. The services are licensed as needed and a single SSN-16 can run four separate services and four instances of the same module or any mix thereof. Assigning or changing a service on an engine only requires a restart of that particular engine and doesn't disrupt the processing on the other engines on the SSN-16.

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