Home > Hyper-V, SCVMM > SCVMM …. Host Reservers and Cluster Reserve

SCVMM …. Host Reservers and Cluster Reserve

What are host reserves?

 Host Reserves define how much of a host’s resources are to reserved for the host operating system. Once these reserves are configured, a virtual machine cannot be deployed on that host if doing so would require the use of those reserved resources. The host resources that may be reserved are as follows:

·         CPU Percentage

·         Memory

·         Disk Space

·         Maximum Disk I/O Per Second (IOPS)

·         Network Capacity Percentage

 Host reserves are specified on a host group basis. In addition, the group reserve settings may also be overridden on a per host basis. To specify the host group reserve settings, right click on the host group name in the Hosts pane, select Properties from the menu and click the Host Reserve Tabs in the Host Group Properties dialog as illustrated in the following figure:

Host-Reverse

 

 

What is cluster reserve ?

Depending on your needs, you can configure a cluster reserve for each host cluster that specifies the number of node failures a cluster must be able to sustain while still supporting all virtual machines deployed on the host cluster. If the cluster cannot withstand the specified number of node failures and still keep all of the virtual machines running, the cluster is placed in an Over-Committed state, and the clustered hosts receive a zero rating during virtual machine placement. The administrator can, during a manual placement, override the rating and place an HAVM on an over-committed cluster.

For example, if you specify a node failure reserve of 2 for an 8-node cluster, the rule is applied in the following ways:

·         If all 8 nodes of the cluster are functioning, the host cluster is marked Over-committed if any combination of 6 nodes (8-2) in the cluster lacks the capacity to accommodate existing virtual machines.

·         If only 5 nodes in the cluster are functioning, the cluster is marked Overcommitted if any combination of 3 (5-2) nodes in the cluster lacks the capacity to accommodate existing virtual machines.

 

VMM’s cluster refresher updates the host cluster’s Over-committed status after each of the following events:

·         A change in the cluster reserve value

·         The failure or removal of nodes from the host cluster

·         The addition of nodes to the host cluster

·         The discovery of new virtual machines on nodes in the host cluster

 

The cluster reserve is set on the General tab of the host cluster properties.

View the status of the cluster, and adjust the cluster reserve.

·         In the Cluster reserve field, specify the maximum number of node failures the cluster must be able to sustain but still keep all existing virtual machines running. If the rule is violated, the host cluster is marked Overcommitted.

 Cluster-Reverse-1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    

 

 How VMM calculate Over-Committed Cluster?!!

 The VMM calculate depending on the highest VM RAM, i.e.. If you have 10 VMs with different RAMs then VMM calculate the amount of RAM by this equation (Highest RAM in VM * N) Where N is the no of VMs in the cluster and equal 10 in our example.

  

Error (13803)

The cluster node failure reserve equals or exceeds the number of nodes in cluster <Cluster Name>

 

Recommended Action

Specify a cluster node failure reserve less than the number of nodes in the cluster and then try the operation again.

 

this is another thing.. due to the fact that building Hyper-V cluster using one physical and one virtual node is not valid (Sure this make no sense). As the VMs cannot failover to the virtual node.

 

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  1. March 23, 2013 at 2:26 pm

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