Lets Design, Implement and do Administration of ESX3

Virtualization with VMWare Infrastructure 3.0

Resource Mgmt Guide -02

Posted by Preetam on March 31, 2007

If a host is added to the cluster, you can no longer create child resource in the host
While creation resource pools, and assigning limits, reservation, shares, if any of the value is not valid, you will see yellow triangle against resource pool.

E.g.You created a resource pool of 10GB, in that you create resource pool of 6 GB and again you try to create resource pool of another 6 GB and type is fixed, you will get yellow triangle

When you move VMs into new resource pool, VMs existing limits & reservations don’t not change. If shares value is customized, it is not changed as well, but it is set to normal.high, low % share value changes. Also unreserved resource values changes to reflect newly added reservations. That being said, if VMs reservations are not met by resource pool, move will fail

When you move hosts into cluster, depending upon what you choose like

  • DRS enabled
  • DRS disabled

Existing resource pools are affected accordingly, when you enable DRS on cluster, you have option of moving the entire tree of resource pool into new cluster or you have option to put this host’s VMs into the cluster’s root resources, when you enable second option, tree structure is changed to flat structure and all VMs & Resource pool becomes child of cluster root, instead of host, However when you happen to move out Host from the cluster, resource pool heirarchy is not moved, in short it becomes completely independent of host.

If DRS is disabled all resource pools are deleted and VMs become direct child of the cluster.

Also in Non-DRS cluster, there is no cluster-wide resource management based on the shares. Shares remain relative to host.

You can create cluster without special license, but you must have a license to enable a cluster for DRS or HA.

What happens to DRS & HA when Virtual center goes down?

HA – Continues to work and can still restart VMs on other hosts in case of failover; however information specific to VMs like cluster properties (priority or isolation response) is based on the state of the cluster before the virtual center goes down

DRS – No recommendations are made for resource optimization.

By default automation level (HA) is enabled at cluster level but you can customize it at VM level as well. Migration recommendation made by VMHA is based on the priority and associated reasons.

When in maintenance mode, the host does not allow you to deploy VMs, VMs that are running on maintenance mode continues to run, you either migrate them to another host or shutdown. When no VMs are running on the host, host’s icon changes to include under maintenance mode. If DRS cluster is in automation mode, all VMs are migrated to different host, when host moved to maintenance mode. This makes sense when other host fails and tries to failover VMs on this host which is in maintenance, being in maintenance mode it won’t allow any VMs. Also if host goes into maintenance mode VMHA will compute current failover capacity excluding host which are in maintenance mode. When host exist maintenance mode, failover capacity is again computed by VMHA.

When you allow VM to be started even if they violate availability constraints deselected (i.e. disable) you will also not able to

  • Reverting VMs to last snapshot
  • Change CPU/Memory reservations
  • Migration VM into the cluster

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