Sometimes, slow SAN performance kills your infrastructure. It can be caused due to multiple issues. This may also require you to sometimes reproduce the problem to identify the issues and to troubleshoot it. Use esxtop to troubleshoot and monitor storage performance from the vSphere host as seen in the earlier chapter. Remove volume caching in order to get the real statistics. Analyze the performance of various I/O sets. You can use free open source tools to measure I/O loads. Use IOMeter available at http://goo.gl/RnDFyS to simulate I/O loads.

Use esxtop while IOMeter is running from a virtual machine and capture the storage performance, for example:

esxtop –a –b 7 –n 700 > performance_data.out

Ensure your multi-path settings are working correctly. Use advanced techniques like Disk Alignment to ensure the data drives are aligned correctly for efficient high I/O. From your SAN, use the built-in tools, if provided, to check the SAN performance as well.