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Introduction:

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This document describes the Cpu/Ram overcommit feature.

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• We will add the cpu and ram overcommit ratios in the cluster_details table. They will be inherited from global settings for cpu over provisioning and for Vmware from memory over provisioning global setting. For othe HVs memory over provisioning will be set as 1.
• vm_details will be populated with the cpu over provisioning and memory over provisioning factors(only for vmware) from global setting. For other HVs memory over provisioning will be set as 1.

Caveats

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What should the behavior be if admin changes the overcommit factor for a cluster that conflicts with the current situation. For example,lets assume Cluster X has an over commit factor of 1.5x for memory and the admin wants to change this to 1x - i.e no overcommit (or changes from 2x to 1.5x) - however, based on the "older" factor, CS might already have assigned more VMs - when the admin reduces the overcommit value value  

1. if there is no conflict, there is no issue

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Note :- The overcommit ratios are dynamically plugged into the capacity calculations. All the capacity calculations is done based on the overcommitted value of capacities. So if the overcommit ratios is decreased the used capacity may go beyond 100%. 
Example:
Overcommit =2 
capacity = 2GB
capacity after overcommit = 4GB.
Now if we deploy 3 VM of 1 GB each 
used =3GB
free = 1GB
used % = 3/4 *100 = 75%
if the overcommit ratio is decreased to 1
used = 3GB
free = -1GB
used % = 3/2 *100 =150% (will generate alerts based on this.)

Alert Generation

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All the alerts are generated based on the global cpu/memory threshold values.

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