Memory recommendations not in alignment with vSphere/vCenter.
Which metric in vSphere/vCenter does "Foglight" use for recommendations under "Optimizer" dashboard?
WORKAROUND:
Foglight uses "Consumed" memory option on the vSphere/ vCenter for recommendations.
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In Optimizer, the consumed memory metric is always used. To base recommendations on active memory would be erroneous and could cause serious problems. To preclude recommending an increase in memory allocation for virtual machines which indicate 100% utilization, the ratio of active memory to consumed is taken into account. If the ratio is large, a memory allocation increase will be recommended. It the ratio is small, no allocation increase will be recommended.
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Basic memory utilization can be measured using two different metrics:
Consumed memory which shows the total amount of memory held by the object at the current time
Active memory which indicates the number of memory pages recently ‘touched’ by the object
Consumed memory is an accurate indication of the memory the virtual machine has. Unfortunately, without getting into the guest OS it is difficult to determine if the virtual machine actually needs and is using all of the memory it.
There are two situations where this is particularly noticeable:
Database servers that are configured to ‘take’ all of the memory available
Servers running ‘Large Pages’ that are not oversubscribed
In both of these situations, consumed memory will sometimes indicate that 100% of the allocation is being utilized. It is, but reducing it may not have adverse effects. Unfortunately, it is impossible to tell without getting into the guest operating system.
Active memory is a good indication of the amount of memory the virtual machine is currently reading or writing but does not take into account the memory pages that have been written but are not currently being accessed. Reducing the memory allocation to a value approaching the active memory value will almost assuredly cause a significant performance impact (swapping).
In Optimizer, the consumed memory metric is always used. To base recommendations on active memory would be erroneous and could cause serious problems. To preclude recommending an increase in memory allocation for virtual machines which indicate 100% utilization, the ratio of active memory to consumed is taken into account. If the ratio is large, a memory allocation increase will be recommended. It the ratio is small, no allocation increase will be recommended.
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