6.5.1

Table 1‑49. 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 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 Rate (KBps)
The Disk Rate chart displays disk read and write rates for LUNs on a host, including average rates.
This chart is located in the Home view of the host Performance tab.
Table 1‑50. Data Counters
Chart Label Description
Read Number of disk read commands completed on each disk on the host, per second. The
aggregate number of all disk read commands is also displayed in the chart.
Read rate = blocksRead per second × blockSize
n
Counter: read
n
Stats Type: Rate
n
Unit: Kilobytes per second (KBps)
n
Rollup Type: Average
n
Collection Level: 3
Write Number of disk write commands completed on each disk on the host, per second.
The aggregate number of all disk write commands is also displayed in the chart.
Write rate = blocksWrien per second × blockSize
n
Counter: write
n
Stats Type: Rate
n
Unit: Kilobytes per second (KBps)
n
Rollup Type: Average
n
Collection Level: 3
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.
vSphere Monitoring and Performance
38 VMware, Inc.