Move the active VMDK to a volume with more spindles or add disks to the LUN. Depending on your hardware, a number greater than 15 ms indicates probable problems with the storage array. The deviceLatency data counter measures the average amount of time, in milliseconds, to complete a SCSI command from the physical device.Check the CPU usage, and increase the queue depth. If the value is greater than 4 ms, the virtual machines on the host are trying to send more throughput to the storage system than the configuration supports. For best performance, the value must be 0 -1 milliseconds. The kernelLatency data counter measures the average amount of time, in milliseconds, that the VMkernel spends processing each SCSI command.You can use the advanced performance charts to view these statistics.
The best ways to determine if your vSphere environment is experiencing disk problems is to monitor the disk latency data counters. If you see a spike in the number of disk read or write requests, check whether any such applications were running then. For example, you might notice a performance degradation with applications that frequently read from and write to the hard disk. Use the disk charts to monitor average disk loads and to determine trends in disk usage. Write rate = blocksWritten per second × blockSize The aggregate number of all disk write commands per second is also displayed in the chart. Number of disk write commands completed on each virtual disk on the virtual machine, per second. Read rate = blocksRead per second × blockSize The aggregate number of all disk read commands per second is also displayed in the chart. Number of disk read commands completed on each virtual disk on the virtual machine, per second. It is available only at collection levels 3 and 4. This chart is located in the Home view of the virtual machine Performance tab. The Disk Rate chart displays disk usage for the virtual machine.
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