HP Surestore Disk Array 12h System Administrator's Guide for HP-UX, MPE, and W - Page 49

HP-UX Using the ARM Command Line Utilities for HP-UX Analyzing Disk Array Performance Selecting a Time Period for Analysis When analyzing performance, you must define the time period over which the analysis will be performed. A starting time (stime) and ending time (etime) establish the analysis period. For the best results, select a time period when performance may be a concern. This will produce the most meaningful analysis and recommendations. For example, if the heaviest load on the disk array occurs between the hours of 8:00 AM and 5:00 PM, restrict the analysis to this time period. If you include periods of less activity, the analysis may yield different results and consequently different recommendations. This occurs because activity is averaged over the entire analysis period, and periods of less activity will offset the effects of busier periods. Typically, you should select a period of time that represents normal system operation. Avoid any unusual events such as a Rebuild or changes made to array capacity. If you select a time period that includes an event that may distort the analysis, the utility will alert you and will not provide any recommendations. You can also control the display interval using the int option. This allows you to control how much detail you get when displaying the metrics. The display interval is the number of 15-minute increments. Checking the Working Set Metric A key factor in monitoring and maintaining optimal performance of the disk array is the Working Set metric. To ensure that disk array performance is maintained, you should access the performance metrics regularly and check the Working Set value. The Working Set performance metric is derived from the Write Working Set parameter. It indicates the ratio of the Write Working Set size to the amount of RAID 0/1 space available. For a detailed explanation of the Write Working Set and its impact on performance, refer to the HP SureStore E Disk Array 12H User's and Service Manual. To maintain performance, the amount of RAID 0/1 space should equal or exceed the Write Working Set, resulting in a Working Set value less than or equal to 1. A Working Set value greater than 1 indicates that the Write Working Set is larger than the available RAID 0/1 space and the disk array is servicing writes from RAID 5 space. If the Working Set consistently exceeds 1, the amount of RAID 0 /1 space available should be increased to improve performance. This can be accomplished in several ways as described in the following section. If the Working Set is consistently much less than 1, some of the RAID 0/1 capacity can be allocated to a new LUN without impacting performance. The remaining RAID 0/1 space should be adequate to accommodate the Write Working Set. 49