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Scaling the infrastructure
Adding or reassigning resources may appropriately address storage array scaling, but these enhancements can be undone by a poorly designed or badly scaled infrastructure. Your network infrastructure, whether it's an FC SAN, the corporate IP network for NAS or an IP SAN, must have the bandwidth and scalability to allow hosts to take advantage of the storage system.

For example, as the amount of data accessed by a host grows, the number of I/O paths (host bus adapters [HBAs] or network interface cards) used by the host may need to be increased--a change that will have to be accommodated by the network. And as a network grows more complex, there are more elements that require attention when attempting to scale storage. For example, if you're using a single inter-switch link (ISL) vs. an ISL trunk, you need to give careful consideration to oversubscription ratios and related matters. Trunks may need to be monitored for saturation. In addition, increasing storage capacity means that the amount of data to be backed up also increases; if you use IP for backups, you may need to perform GigE aggregation to allow for greater I/O.

Scaling storage requires a more holistic approach, where the considerations go beyond the storage array itself. For example, let's assume you have a 3TB

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database with peaks of 40,000 IOPS. You expect a 40% growth rate for both the disk and I/O over the next three or four years. The amount of I/O dedicated to only this database could outgrow most small arrays, making a forklift upgrade almost unavoidable. But even if you're able to upgrade the storage array to handle the higher capacity and performance requirements, will you be able to scale to handle the increased loads?

It's important to monitor an array's network utilization at all times. Use network monitoring tools to keep a constant watch on how much network traffic is generated by the array. Key network indicators are input and output errors, retransmissions, line loss and saturation, and latency. Make use of both horizontal and vertical spreads to minimize network imbalance. For example, if it's a NAS or IP SAN solution, make sure your array is connected to multiple switches and that the client load is evenly distributed.

This was first published in June 2006

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