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Tip 2. Know what's going on
After you've developed a good picture of the components in your storage network infrastructure, the next step is to fully understand what those devices are doing at a particular moment in time. Many switch and HBA vendors build some of these capabilities into their products. But instead of going to each device to see its view of traffic conditions, it may be better to find a tool that can provide consolidated real-time feedback on how data is traversing your network. There are software solutions and physical layer access tools that can report on the infrastructure traffic. The tools that can monitor network devices specifically are important because, as all of our experts pointed out, there are situations where operating systems or applications report inaccurate information when compared to what the device is reporting.
These tools can be used for trend analysis and, in some cases, they can simulate an upcoming occurrence of a data storage infrastructure problem. For example, if an ISL is seeing a steady increase in traffic (see Tip 6), the ability to trend that traffic growth will help identify how soon an application rebalance or an increase in ISL bandwidth will be required. Other tools will report on CRC or packet errors to ports, which can indicate an upcoming SFP failure.
Tip 3. Know what you want to do
With your inventory complete and good visibility into your SAN established, the next
Tip 4. Limit the impact
When you feel you're at the stage where you're ready to make changes to the environment, the next step is to limit the sphere of impact as much as possible by subdividing the SAN into virtual SANs (VSANs).
Subdividing (in a worst-case scenario) changes made to the environment that yield unexpected results, like preventing a server from accessing storage or even causing an outage, will have limited repercussions across the infrastructure. Limiting the sphere of impact is by itself an important fine-tuning step that will help create an environment that's more resilient to changes in the future, and can help contain problems. For example, an application may suddenly need an excessive amount of storage resources; subdividing the SAN will help contain it and keep the rest of the infrastructure from being starved. This aspect of fine-tuning shouldn't require any new purchases as it's a setup and configuration process.
Tip 5. Test to learn, learn to test
Although it may seem to be something of a luxury, one key to fine-tuning is to have a permanent testing lab that can be used to try out proposed changes to the environment or to simulate failed conditions. Lab testing lets you explore the alternatives and develop remedies without impacting the production network. In speaking with our experts, and in our own experience, most SAN emergencies result from implementing a new feature in the storage array or on the SAN. If you lack the resources to create a lab environment, an alternative may be to work with your infrastructure vendors, as many have facilities that can be used to recreate problems or to test the implementation of new features.
Storage I/O performance is typically high on a fine-tuning top 10 list, and although it didn't make it into our top five tips, it rounds out the rest of the list. Before performance issues are tackled, it's important that the environment be documented, understood and made as resilient as possible. While slow response time due to lack of performance tuning is a concern, zero response time because of poor planning is a lot worse.
This was first published in September 2010