HP ProLiant 4500 Disk Subsystem Performance and Scalability - Page 30

ECG025.0997 WHITE PAPER (cont.) ... Disk-Related Measurement Terms Within this document we discussed disk-related performance characteristics and how these measurement terms can affect the performance of an entire disk subsystem. Understanding how a hard disk works and the measurement terms used in the industry provides insight on the possible affect(s) disks can have on the entire disk subsystem. For example, if your average access time on the hard disk is poor, it can become a bottleneck. Thus causing poor performance throughout the disk subsystem because other components are waiting on the slowest device, which in this example is the hard disk. Understanding the Transfer Rates within the Disk Subsystem We also discussed in detail each part of the disk subsystem and how it all works together using different transfer rates. Knowing the integral parts of the disk subsystem and how they transfer data from one component to another helps you quickly identify potential bottlenecks. The slowest component in the disk subsystem generally determines the overall throughput of the system. The Importance of File System Cache Improving performance on a disk subsystem comes with understanding the impact of file system caching. File system cache is the single fastest component within the disk subsystem; therefore, we know that this device is the least likely of all the disk subsystem components to be a performance bottleneck. If this device did become a bottleneck, however, simply add more memory to the server. This is a great way to improve disk subsystem performance. Benefits of Scaling Throughout this paper we learn through many examples that scaling or adding more hardware to your disk subsystem typically provides better system performance. Listed below are the scaling benefits we discovered during our testing. • Eliminates bottlenecks • Increases I/O concurrency • Increases cumulative transfer rate • Decreases idle time on the controller • Increases cumulative disk capacity • Increases disk controller cache Your goal is to produce the right balance for an effective high-performing disk subsystem. It is for you to choose which level or mixture of scaling is right for your environment. The test results and data contained in this paper should help you with that choice. 30