96 Maintaining a Storage ArrayPerformance TuningOver time, as a storage array exchanges data between the hosts and physicaldisks, its performance can degrade. Monitor the performance of a storagearray and make adjustments to the storage array operational settings toimprove performance.Monitoring PerformanceMonitor the performance of a storage array by using the save storageArrayperformanceStats command. This command saves performance informationto a file that you can review to determine how well the storage array isrunning. Table 6-1 lists the performance information saved to the file.Table 6-1. Storage Array Performance InformationType of Information DescriptionDevices Devices are:• RAID Controller Modules — The RAID controller modulein slot 0 or 1 and a list of the virtual disks owned by theRAID controller module• Virtual Disk — A list of the virtual disk names• Storage Array Totals — A list of the totals for both RAIDcontroller modules in an active-active RAID controllermodule pair, regardless if one, both, or neither are selectedfor monitoringTotal I/Os Number of total I/Os performed since the storage array wasstartedRead Percentage Percentage of total I/Os that are read operations (calculatethe write percentage by subtracting the read percentage from100 percent)Cache Hit Percentage Percentage of reads that are fulfilled by data from the cacherather than requiring an actual read from a physical diskCurrent KB/second Current transfer rate in kilobytes per second (current meansthe number of kilobytes per second since the last time thepolling interval elapsed, causing an update to occur)Maximum KB/second Highest data transfer value achieved in the currentkilobyte-per-second statistic block
