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Pros and cons: Appliances, PBAs and intelligent switches

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Introducing SPAID
An intelligent switch is typically characterized by specialized hardware and processing capability at the port level. This makes the data path processing highly distributed and therefore efficient and scalable. In concept, the agent code that resides in the host in an out-of-band solution, now can reside on or near these ports, eliminating the need for code on the hosts. The amount of processing power placed at the port level, and whether the metadata is placed in one location or another, determines the architectural differences of various intelligent switches. Depending on the implementation, the control path software can be installed on a blade inside the switch or externally on a separate piece of hardware.

In a nutshell, an intelligent switch can offer in-band simplicity and out-of-band scalability. It splits the data path from the control path and eliminates the requirement for host-level code. This is called SPAID, an architecture that will become the most popular way to deliver high-performance storage services from the fabric.

The SPAID architecture:

  • Separates the control path from the data path.
  • Possesses an independent metadata server.
  • Leverages port-level processing capabilities of intelligent switches or purpose-built controllers.
  • Allows for independent scaling of the control and data path processing.

EMC is expected to deliver a software product code-named Storage Router. It will leverage the SPAID concept on multiple intelligent switch and director platforms, including those from Brocade, Cisco and McData. It's fundamentally a virtualization application at the foundation layer, with a variety of other applications built on top of it, most notably heterogeneous data migration.

In Cisco terminology, the application would run on a service module inside a Cisco MDS 9000, and the control path/metadata server functions would be provided by an appliance outside the switch, or as a blade inside the switch. Both can be scaled independently for exceptional performance. Vendor implementations

Despite the hype created by the pioneers of intelligent switches such as Rhapsody (now Brocade) and Sanera (now McData), there aren't many products available. Brocade's intelligent switch should ship soon, with McData's coming in nine or more months.

Maxxan is currently the clear intelligent switch leader, followed closely by Cisco. Maxxan has implemented significant computational performance at the port level by using an off-the-shelf Intel network processor rather than designing an ASIC.

Cisco based its MDS 9000 family on an in-house- developed ASIC that's implemented at every port. In addition, Cisco offers a series of service modules (application blades) where the application runs. For IBM Storage Virtualization Controller, Cisco implemented a Cache Services Module. For Veritas Volume Manager's port (called Veritas Storage Foundation for Networks) they implemented an Advanced Services Module (ASM). It's noteworthy that each application requires its own unique Service Module. Cisco has also created an innovative software product called the MDS 9000 Data Tap Service that runs on an ASM inside the switch and allows a regular appliance-based application (e.g., FalconStor IPStor) to run significantly faster.

In the purpose-built category, Troika and Candera both have ASIC-based, high-performance platforms designed to run applications in the fabric. Not being switch vendors, they can focus on working with all legacy switch vendors equally well and stay focused on application integration.

The movement of intelligence to the fabric is a given because the benefits are apparent. This is a great time to start planning for the movement of intelligence into your storage fabric.

This was first published in October 2004

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