OS alert and Vcentre alert

We have a monitoring tool to monitor our servers for cpu , memory, disk ect. This  tool uses wmi and monitor the servers at os level.
This monitoring tool is throwing an alert for a server's cpu recently. This server is a VM.
I do not see any alarm on the vcenter for esxi host or for the vm.
I believe that the esxi host has enough resources to give its vm since i do not receive any alert fro vcentre, i might be wrong.
Should I have to increase the cpu core/memory to avoid the alert?
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You might be able to assess the alert by comparing the time of the alert with the CPU Usage graph you can get from vCenter.

The WMI monitor is going to be using triggers based on the guest's view of things while vCenter can show you the hypervisor's idea of how much CPU the guest is using. They may have exactly the same trigger values, but one may alert while the other one does not, because of these different views.

In general, if you see a guest with only occasional short spikes to 100% CPU usage, that may not represent a problem unless the busyness results in observable response-time lagging for the guest's workload -- that would have to be measured differently. And some systems will be designed so that certain guests are allowed to use 100% of their quantum all the time, perhaps so they can perform lower-priority batch tasks when none of the other guests are too busy. You won't necessarily find an approach where one size fits all cases.
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Your monitoring tool probably does not know that the machine your are monitoring is a VM!

Look at the VMware vSphere stats!, the WMI stats are probably wrong!

see my EE Article

HOW TO:  Performance Monitor vSphere 4.x or 5.0

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SandeepSr System AdministratorCommented:
I agree with above comment where the Monitoring tool could go wrong while collecting data and due to which alert is getting trigger wrongly.
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sara2000Author Commented:
Thank you for your reply, Andrew thank you for the link.
Here is something I noticed, hope you can help me on this.
I enabled memory alert at vcenter for both Hosts and VMs for 90%. I get alerts for both esxi and vm.
I enabled DRS and DRS setting is at full automation.
Here I was expecting the vm to move from the esxi which has higher memory utilization(90%) to another, but I do not see any vm migration.
Does this mean that other esxi hosts do not have enough memory to take this vm?
I know the DRS functions because I set the rule to few vms to stay at few esxi only , they were migrated to those esxi hosts.
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
DRS is not a load balancer, it will move VMs automatically, when the hosts are under pressure.

Also you may want to change the DRS settings to Aggressive. (and move the slider to the end!)
sara2000Author Commented:
I am confused with ballooning and DRS. hope you can explain?
For an example we allocate 4GB for a vm, the vm will get that amount from its hosting esxi host, in the meantime other vms will try to get their memory from its host. if there is not enough memory at the esxi
 Will the DRS move a vm to another host
VM will go into ballooning?
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
I think this question, is going off topic.

Please post a new question, and myself or other experts will be glad to assist.
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