6.7

Table 1‑57. Disk I/O Performance Enhancement Advice (Continued)
# Resolution
8 For resource-intensive virtual machines, separate the virtual machine's physical disk drive from the drive with the system
page file. 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
file.
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 (ms)
The Disk (ms) chart displays the amount of time taken to process commands on a host.
This chart is located in the Home view of the host Performance tab.
Table 1‑58. Data Counters
Chart Label Description
Highest Disk Latency Highest latency value of all disks used by the host.
Latency measures the time used to process a SCSI command issued by the guest OS to the virtual
machine. The kernel latency is the time VMkernel takes to process an I/O request. The device latency
is the time it takes the hardware to handle the request.
Total latency = kernelLatency + deviceLatency.
n
Counter: maxTotalLatency
n
Stats Type: Absolute
n
Unit: Milliseconds (ms)
n
Rollup Type: Latest (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 configuration supports. Check the CPU usage, and
increase the queue depth.
vSphere Monitoring and Performance
VMware, Inc. 50