6.7

Table Of Contents
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The value for the deviceLatency data counter is greater than 15 ms indicates that there are probably
problems with the storage array.
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The queueLatency data counter measures above zero.
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Spikes in latency.
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Unusual increases in read/write requests.
Cause
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The virtual machines on the host are trying to send more throughput to the storage system than the
configuration supports.
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The storage array probably is experiencing internal problems.
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The workload is too high and the array cannot process the data fast enough.
Solution
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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.
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Move the active VMDK to a volume with more spindles or add disks to the LUN.
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Increase the virtual machine memory. It should allow for more operating system caching, which can
reduce I/O activity. Note: It may require you to 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.
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Check swap statistics in the guest operating system to verify that virtual machines have adequate
memory. 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.
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Defragment the file systems on all guests.
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Disable antivirus on-demand scans on the VMDK and VMEM files.
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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.
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Use Storage vMotion to migrate I/O-intensive virtual machines across multiple hosts.
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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.
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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.
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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.
vSphere Monitoring and Performance
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