HP ProLiant 4500 Disk Subsystem Performance and Scalability - Page 19

ECG025.0997 WHITE PAPER (cont.) ... Lastly, our one controller testing shows that once we added another four drives to our test environment (8 to 12 drives), the increase in performance was 25%, as shown in Figure 8. Summary of Findings - Like Drive Scaling Doubling the number of drives in our system, in either a RAID 0 or 5 environment, increased performance by more than 50% when using 2 or 4GB drives. Also, by adding four more drives to our environment (making a total of 12 drives) as shown in Figure 8, we learned that our performance gain increased another 25%. However, keep in mind that by doubling our drives in our test environment we improved performance, but we also doubled the drive cost for this configuration. If performance is a concern, this is an effective solution for your environment. To help assist you in deciding what is right for your environment, Table 8 lists some advantages and disadvantages of like drive scaling. Table 8: Like Drive Scaling Advantages and Disadvantages Advantages Disadvantages Eliminates bottlenecks because you minimize seek time. Drive cost increases each time you add more drives. Increases I/O concurrency because you have more drives processing disk requests. Using smaller size drives limits your maximum capacity per controller. For example, the Compaq SMART-2 Array Controller supports up to 14 drives. By using fourteen 2GB drives, your data capacity equals 28GB. By using fourteen 4GB drives, your data increases to 56GB. Increases cumulative transfer rate because the more drives you add to your system the more data can be transferred. By adding more drives to your system you have more disks to manage, thus increasing the probability of disk failure. Idle time on the controller decreases because cumulative disk performance increases. LIKE CAPACITY SCALABILITY Like capacity scaling, unlike like drive scaling, is when you use similar or "like" drives and scale them to determine if your environment needs multiple lower capacity drives or fewer larger capacity drives. For example, if you need four Gigabytes of disk storage, what should you purchase to meet your capacity requirements and provide the best system performance? Should you buy one 4.3-Gigabyte drive or two 2.1-Gigabyte drives? If you currently have hard drives in your environment that are not using the total storage capacity of the disk, using like drives with a smaller capacity might be the right solution for you. 19