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An administrator receives a complaint that a virtual machine is performing poorly. The user attributes the issue to poor storage performance.
If the storage array is the bottleneck, which two counters would be higher than normal? (Choose two.)
A. Average ESXi VMKernel latency per command, in milliseconds (KAVG per cmd)
B. Average device latency per command, in milliseconds (DAVG per cmd)
C. Average virtual machine operating system latency per command, in milliseconds (GAVG per cmd)
D. Number of SCSI reservation conflicts per second (CONS per second)
Correct Answer: BD
Explanation/Reference:
http://communities.vmware.com/docs/DOC-9279
Section 4.2.2
DAVG – This is the latency seen at the device driver level. It includes the round trip time between the HBA and the storage. DAVG is a good indicator of performance of the backend storage
KAVG has to do with kernel queues, so it’s not relevant.
GAVG = DAVG + KAVG, but we already monitor DAVG, so this won’t give is anything extra as info
Section 4.2.10 Reservation Statistics
CONS/s The number of SCSI reservation conflicts per second.
During the conflict period any I/O going to the LUN will fail with the BUSY status, and will have to be retried. Usually reservations are held for a very short time (few hundred microseconds). Obviously high number of reservation conflicts is not good and I/O latencies will go up when there are retries. Likelihood of having reservation conflicts increases with the number of metadata operations and with the number of ESX hosts sharing the same LUN doing I/O at the same time
