Scale your SAN for tomorrow

Characterizing SAN scalability for today and tomorrow.

This tip is excerpted from the white paper "Scaling the SAN heights" from Sanera Systems, Inc.

Enterprises are increasingly adopting storage area network (SAN) technology to increase the availability of their mission critical data. Ironically, the very reason enterprises are deploying SANs (i.e. scalability) is in Christensen's "classic undershoot" of technology innovation.

SAN scalability is currently characterized as bi-dimensional, or scale up/scale out. Today, "scale up" takes a costly equipment-centric approach to optimize the problem of managing additional physical ports and switches in a growing fabric. Ideally, it should aim to increase the number of available paths between any nodes in a fabric.

Similarly, the current approach to scaling out the fabric is equally equipment-centric as it simply tries to attach a remote device to the SAN fabric. Ideally, the scale-out approach should aim to manage the logistics of resource sharing over the long distance network, thereby increasing the data integrity in long-distance SANs.

SAN scalability should be characterized in dimensions beyond scale-up/scale out. One such dimension of SAN scalability is the data transfer rate in the SAN. Currently, the Fibre Channel SAN networks run at 2Gbps or 200M bytes/sec. If we fast forward to only a few years from now, we see the SANs becoming the data backbone of the enterprise.

In such a data center, we would expect to see the same ratio of computing horsepower to data transfer rate ratio that we see today in the high-end computing equipment. This ratio today is around 100. Assuming a data center that processes 1TFLOPs/sec (trillion instructions per second) we should expect that data transfer rates between nodes should approach 2G bytes/sec. An alternate view of this trend is that the amount of data an application can store on a SAN is limited not by the storage capacity of the SAN (number of concurrent nodes on a SAN) but the amount of latency tolerated by the application writing the data.

Today, SAN scalability is often characterized by the amount of storage capacity that can be added to the SAN. In the future, SAN scalability will be characterized not just by the storage capacity but also the data transfer rate to and from from the SANs. Link speeds would therefore need to scale far beyond the current 2G bits/sec to make the SAN usable by demanding mission critical applications.


About the author: Patrick Harr is vice president of marketing at Sanera Systems, Inc. (Sunnyvale, California), www.sanera.net.

This was first published in January 2003

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