SAN-based intelligence: the Holy Grail of storage management? - Storage Networking - storage area networks

Computer Technology Review, Dec, 2003 by Bill Terrell

The buzz around "SAN-based intelligence" has sparked a lot of interest, according to recent polls of storage administrators. In spite of the dearth of real products, the major fabric infrastructure vendors and storage equipment vendors have been posturing themselves to capture mind share and the perception of leadership. But is there real value and viable solutions to SAN storage management headaches in this so-called network-based "intelligence"?

The SAN storage management puzzle today consists of many pieces including resource discovery, capacity planning, performance and availability tuning, provisioning, backup and recovery, disaster protection, and change management. Since data growth and application requirements are expanding so quickly, storage management can become a costly and painfully vicious cycle. Today's tools consist of host-based software such as volume managers, and array-based services like replication that don't work cooperatively together. Also, these services usually only work between homogeneous host-servers or storage systems locking users into a particular vendor with a specific roadmap. Keeping up with the plethora of management interfaces, software versions, and configurations only adds to the management complexity.

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Centralizing and consolidating storage management services into a single layer that works across heterogeneous host-servers and storage systems is the proposed benefit of providing services in the network via "intelligent" purpose-built devices. The types of possible services include provisioning from a common pool of physical storage for better storage utilization, data replication between heterogeneous physical storage systems, performance information to tune configurations, remote asynchronous replication for distributing services like backup or for disaster protection, emerging advanced capabilities like dynamic data migration between different classes of storage (enabling Information Lifecycle Management), and changing the backup/recovery paradigm altogether with continuous backup and instant recovery services. Imagine the possible time and cost savings if managers could invoke all these capabilities from a single console and have them work with any servers or storage.

Sounds great, right? But how do we get there from here?

We won't get there very soon with so-called "intelligent" switches from the major vendors. Most have indicated that products won't be ready until 2004 or 2005. And even then, the capabilities are likely to be too basic to begin with. There are also products with fairly rich feature sets shipping today on so-called SAN appliances. However, since those solutions basically run on generic PC servers with HBAs, and reside in-band between application servers and storage systems, you'd better be sure you've got the scalability and reliability needed--not just for today, but for the next few years. That is, unless you're prepared to swap them out and start over again later. And, at the end of the day, a server with the processor horsepower, amount of memory, and quantity of HBAs needed for even modest-sized SANs can be quite costly.

One advantage of the appliance model is that it is not a fabric switch. The port personality of these appliances is that of a logical end-point like an HBA in a host server or a port on a storage array. That means you can add appliances to an existing SAN without disrupting the fabric. The downside of "intelligent" switches is that they are switches and are subject to the same interoperability concerns that exist today with fabric switches. What if you could deploy SAN-based storage services on an appliance-like platform that is fabric agnostic but has the performance, scalability, and reliability of fabric switches?

A new category of purpose-built appliances for hosting storage services in the SAN is coming on the market now--the Network Storage Services Platform. An NSS Platform is like an appliance in that the ports it provides are termination end-points, it is fabricagnostic, and can be installed non-disruptively in existing SANs. Unlike the appliance, though, the NSS Platform is built using custom hardware that provides a scalable number of ports with the performance and reliability of a fabric switch. An NSS Platform in the data-path between hosts and their storage should be just a "bump in the wire"--no different than a fabric switch.

The first NSS Platform-based storage service required for SAN-based intelligence is providing a target server at each port that logically terminates the I/O traffic like a virtual storage array head. Each target port of the NSS Platform can then be configured to export virtual disks (LUNs) to host servers using access control lists to ensure security. This "virtualization" layer has been hyped as the solution to the SAN storage management problem. But, in reality, "storage virtualization" is just the necessary enabling technology on which to layer services such as path management, volume management, replication, statistics monitoring, mirroring, and journaling.