Use the Performance Monitor data to make tuning decisions, as described in this table.
Data | Implications for Performance Tuning |
---|---|
Total I/Os |
This data is useful for monitoring the I/O activity of a specific and a specific , which can help identify possible high-traffic I/O areas. If the I/O rate is slow on a logical drive, try increasing the size by selecting Array >> Add Free Capacity (Disk Drives) . You might notice a disparity in the total I/Os (workload) of controllers. For example, the workload of one controller is heavy or is increasing over time while that of the other controller is lighter or more stable. In this case, you might want to change the controller ownership of one or more logical drives to the controller with the lighter workload. Use the logical drive total I/O statistics to determine which logical drives to move. You might want to monitor the workload across the storage subsystem. Look at the Total I/Os column of the Storage Subsystem Totals row in the Performance Monitor window. If the workload continues to increase over time while application performance decreases, you might need to add additional storage subsystems. By adding storage subsystems to your enterprise, you can continue to meet application needs at an acceptable performance level. |
Read Percentage |
Use the Read Percentage for a logical drive to determine actual application behavior. If a low percentage of read activity exists relative to write activity, you might want to change the level of an array from to to obtain faster performance. |
Cache Hit Percentage |
A higher cache hit percentage is desirable for optimal application performance. A positive correlation exists between the cache hit percentage and the I/O rates. The cache hit percentage of all of the logical drives might be low or trending downward. This trend might indicate inherent randomness in access patterns. In addition, at the storage subsystem level or the controller level, this trend might indicate the need to install more controller if you do not have the maximum amount of memory installed. If an individual logical drive is experiencing a low cache hit percentage, consider enabling dynamic cache read for that logical drive. Dynamic cache read prefetch can increase the cache hit percentage for a sequential I/O workload. |
Current KB/s and Maximum KB/s |
The transfer rates of the controller are determined by the application I/O size and the I/O rate. Generally, small application I/O requests result in a lower transfer rate but provide a faster I/O rate and shorter response time. With larger application I/O requests, higher throughput rates are possible. Understanding your typical application I/O patterns can help you determine the maximum I/O transfer rates for a specific storage subsystem. Consider a storage subsystem equipped with controllers that support a maximum transfer rate of 100 MB/s (100,000 KB/s). Your storage subsystem typically achieves an average transfer rate of 20,000 KB/s. The typical I/O size for your applications is 4 K, with 5,000 I/Os transferred per second for an average rate of 20,000 KB/s. In this case, I/O size is small. Because system overhead is associated with each I/O, the transfer rates do not approach 100,000 KB/s. However, if your typical I/O size is large, a transfer rate within a range of 80,000 to 90,000 KB/s might be achieved. Wide Ultra SCSI supports sustained data transfer rates of up to 40 MB/s with large I/O sizes. The maximum transfer rates with relatively small I/O sizes, 4096 bytes, is approximately 17 MB/s. |
Current IOPS and Maximum IOPS |
Factors that affect input/output operations per second (IOPS) include these items:
The higher the cache hit rate, the higher I/O rates will be. Performance improvements caused by changing the segment size can be seen in the IOPS statistics for a logical drive. Experiment to determine the optimal segment size, or use the file system or database block size. Higher write I/O rates are experienced with enabled compared to disabled. In deciding whether to enable write caching for an individual logical drive, look at the current IOPS and the maximum IOPS. You should expect to see higher rates for sequential I/O patterns than for random I/O patterns. Regardless of your I/O pattern, you should enable write caching to maximize the I/O rate and shorten the application response time. |