ABSTRACT
This chapter focuses on existing storage systems and resolving performance problems, rather than on performance engineering/sizing for new systems. Resolving performance problems on systems you already own is significantly less expensive than buying new systems. Performance problems can and do impact business revenues or customer service. Systems can be over-engineered for the performance needs of the largest and most demanding applications, then overdesigned to account for future growth and increased application demand on the system. Excessive paging also occurs when creating a load that exceeds the ability to get that information off the disk and into memory. Applications group input/output (I/O) into chunks to be sent to the storage or requested from the storage. The root cause of performance problems often involve multiple loads. Storage arrays include cache to speed up performance. The better storage arrays include robust, protected caching, including mirrored caching across duplex storage array I/O controllers to deal with single I/O controller failure without data loss.
