6.7

Table 1‑61. Disk I/O Performance Enhancement Advice (Continued)
# Resolution
3 Disable antivirus on-demand scans on the VMDK and VMEM files.
4 Use the vendor's array tools to determine the array performance statistics. When too many servers simultaneously access
common elements on an array, the disks might have trouble keeping up. To increase throughput, consider array-side
improvements.
5 Use Storage vMotion to migrate I/O-intensive virtual machines across multiple hosts.
6 Balance the disk load across all physical resources available. Spread heavily used storage across LUNs that are accessed
by different adapters. Use separate queues for each adapter to improve disk efficiency.
7 Configure the HBAs and RAID controllers for optimal use. Verify that the queue depths and cache settings 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 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.
Memory (%)
The Memory (%) chart displays host memory usage.
This chart is located in the Home view of the host Performance tab.
Chart Analysis
To ensure best performance, the host memory must be large enough to accommodate the active memory
of the virtual machines. The active memory can be smaller than the virtual machine memory size. It
allows you to over-provision memory, but still ensures that the virtual machine active memory is smaller
than the host memory.
Transient high-usage values usually do not cause performance degradation. For example, memory usage
can be high when several virtual machines are started at the same time or when a spike occurs in virtual
machine workload. However, a consistently high memory usage value (94% or greater) indicates that the
host is probably lacking the memory required to meet the demand. If the active memory size is the same
as the granted memory size, the demand for memory is greater than the memory resources available. If
the active memory is consistently low, the memory size might be too large.
If the memory usage value is high, and the host has high ballooning or swapping, check the amount of
free physical memory on the host. A free memory value of 6% or less indicates that the host cannot
handle the demand for memory. It leads to memory reclamation, which might degrade performance.
vSphere Monitoring and Performance
VMware, Inc. 53