A vSphere HA cluster with four hosts has admission control configured to tolerate one host failure.
Which statement is true if a fifth host is added?
A.
CPU and Memory capacity will be set to 50%.
B.
CPU and Memory capacity will be set to 30%.
C.
CPU and Memory capacity will be set to 25%.
D.
CPU and Memory capacity will be set to 20%.
Explanation:
Select the Percentage of Cluster Resources Reserved admission control policy. This policy offers the most
flexibility in terms of host and virtual machine sizing. When configuring this policy, choose a percentage for
CPU and memory that reflects the number of host failures you want to support. For example, if you want
vSphere HA to set aside resources for two host failures and have ten hosts of equal capacity in the cluster, then
specify 20%
https://pubs.vmware.com/vsphere-51/index.jsp?topic=%2Fcom.vmware.vsphere.avail.doc%
2FGUID-39731BEC-EB0C-48C9-813B-CAF9DE884FD5.html
D is correct, as there has to be a reservation of 100% / 5 Hosts to compensate one host failure. Thats exactly 20%.
4 Hosts had the reservation of 25%, to compensate a single host failure.
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To clarify:
To tolerate 1 host failure, you have to reserve 1/4 x 100% = 25% of CPU & RAM on each host.
After another host is added.
To tolerate 1 host failure, you have to reserve 1/5 x 100% = 20% of CPU & RAM on each host.
Adding more hosts while keeping the failure tolerance same means you would need to reserve less for failure capacity.
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Updated URL: https://docs.vmware.com/en/VMware-vSphere/6.5/com.vmware.vsphere.avail.doc/GUID-39731BEC-EB0C-48C9-813B-CAF9DE884FD5.html
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