6.5.1

Table 1‑57. Disk I/O Performance Enhancement Advice (Continued)
# Resolution
6 Balance the disk load across all physical resources available. Spread heavily used storage across LUNs that are
accessed by dierent adapters. Use separate queues for each adapter to improve disk eciency.
7 Congure the HBAs and RAID controllers for optimal use. Verify that the queue depths and cache seings on the
RAID controllers are adequate. If not, increase the number of outstanding disk requests for the virtual machine by
adjusting the Disk.SchedNumReqOutstanding parameter. For more information, see vSphere Storage.
8 For resource-intensive virtual machines, separate the virtual machine's physical disk drive from the drive with the
system page le. It alleviates disk spindle contention during periods of high use.
9
On systems with sizable RAM, disable memory trimming by adding the line MemTrimRate=0 to the virtual
machine's VMX le.
10 If the combined disk I/O is higher than a single HBA capacity, use multipathing or multiple links.
11 For ESXi hosts, create virtual disks as preallocated. When you create a virtual disk for a guest operating system,
select Allocate all disk space now. The performance degradation associated with reassigning additional disk space
does not occur, and the disk is less likely to become fragmented.
12 Use the most current host hardware.
Disk (KBps)
The Disk (KBps) chart displays disk usage for the 10 virtual machines on the host with the most disk usage.
This chart is located in the Virtual Machines view of the host Performance tab.
Table 1‑58. Data Counters
Chart Label Description
virtual_machine Sum of the data read from the virtual machine.
n
Counter: usage
n
Stats Type: Rate
n
Unit: KiloBytes per second (KBps)
n
Rollup Type: Average (Minimum/Maximum)
n
Collection Level: 1 (4)
Chart Analysis
Use the disk charts to monitor average disk loads and to determine trends in disk usage. For example, you
might notice a performance degradation with applications that frequently read from and write to the hard
disk. If you see a spike in the number of disk read or write requests, check whether any such applications
were running then.
The best ways to determine if your vSphere environment is experiencing disk problems is to monitor the
disk latency data counters. You can use the advanced performance charts to view these statistics.
n
The kernelLatency data counter measures the average amount of time, in milliseconds, that the
VMkernel spends processing each SCSI command. For best performance, the value must be 0 -1
milliseconds. 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 conguration supports. Check the CPU usage, and increase
the queue depth.
n
The deviceLatency data counter measures the average amount of time, in milliseconds, to complete a
SCSI command from the physical device. Depending on your hardware, a number greater than 15 ms
indicates probable problems with the storage array. Move the active VMDK to a volume with more
spindles or add disks to the LUN.
vSphere Monitoring and Performance
44 VMware, Inc.