6.0.1

Table 1‑52. Disk I/O Performance Enhancement Advice (Continued)
# Resolution
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 (Number)
The Disk (Number) chart displays maximum queue depth for the top ten LUNs on a host.
This chart is located in the Home view of the host Performance tab.
Table 1‑53. Data Counters
Chart Label Description
Maximum Queue Depth Maximum queue depth. Queue depth is the number of commands the SCSI driver
queues to the HBA.
n
Counter: maxQueueDepth
n
Stats Type: Absolute
n
Unit: Number
n
Rollup Type: Average
n
Collection Level: 1
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 at that time.
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 should be 0-1
milliseconds. If the value is greater than 4ms, 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
42 VMware, Inc.