6.7

Table 1‑100. CPU Performance Enhancement Advice (Continued)
# Resolution
5 Increase the CPU shares to give the virtual machine more opportunities to run. The total ready time on the host might remain
at the same level if the host system is constrained by CPU. If the host ready time doesn't decrease, set the CPU reservations
for high-priority virtual machines to guarantee that they receive the required CPU cycles.
6 Increase the amount of memory allocated to the virtual machine. This decreases disk and or network activity for applications
that cache. This might lower disk I/O and reduce the need for the host to virtualize the hardware. Virtual machines with
smaller resource allocations generally accumulate more CPU ready time.
7 Reduce the number of virtual CPUs on a virtual machine to only the number required to execute the workload. For example, a
single-threaded application on a four-way virtual machine only benefits from a single vCPU. But the hypervisor's maintenance
of the three idle vCPUs takes CPU cycles that could be used for other work.
8 If the host is not already in a DRS cluster, add it to one. If the host is in a DRS cluster, increase the number of hosts and
migrate one or more virtual machines onto the new host.
9 Upgrade the physical CPUs or cores on the host if necessary.
10 Use the newest version of hypervisor software, and enable CPU-saving features such as TCP Segmentation Offload, large
memory pages, and jumbo frames.
Disk (KBps)
The Disk (KBps) chart displays disk usage for the virtual machine.
It is located in the Home view of the virtual machine Performance tab.
Table 1‑101. Data Counters
Chart Label Description
Usage Average data I/O rate across all virtual disks on 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 configuration supports. Check the CPU usage, and
increase the queue depth.
vSphere Monitoring and Performance
VMware, Inc. 80