6.0.1

If the disk latency values are high, or if you notice other problems with disk I/O performance, consider
taking the actions listed below.
Table 1‑99. Disk I/O Performance Enhancement Advice
# Resolution
1 Increase the virtual machine memory. This should allow for more operating system caching, which can reduce I/O
activity. Note that this might require you to also increase the host memory. Increasing memory might reduce the
need to store data because databases can utilize system memory to cache data and avoid disk access.
To verify that virtual machines have adequate memory, check swap statistics in the guest operating system.
Increase the guest memory, but not to an extent that leads to excessive host memory swapping. Install VMware
Tools so that memory ballooning can occur.
2 Defragment the file systems on all guests.
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. Consider array-side improvements
to increase throughput.
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. This 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 Rate (KBps)
The Disk Rate chart displays disk usage for the virtual machine.
This chart is located in the Home view of the virtual machine Performance tab. It is available only at
collection levels 3 and 4.
Chapter 1 Monitoring Inventory Objects with Performance Charts
VMware, Inc. 71