Use host-based VM placement to tie your VMs more closely to your infrastructure. By using vCenter Server to tag hosts and VMs with specific tags, you make certain that when the system runs an optimization, it uses VM-to-host tag matching to ensure that VMs are moved to - or stay with - the appropriate host.
Using Tags to Enhance Structure
When configuring data centers or custom data centers without tags, you configure clusters and their hosts as relatively homogenous. All cluster resources must support, for example, the same OS or the same security requirements so that optimization actions do not place VMs in the wrong cluster.
The tagging approach enables you to define zones of infrastructure within cluster boundaries. VM-to-cluster tagging, for example, allows you to tag VMs and clusters to assure that Windows VMs are moved only to Windows-licensed clusters and Oracle VMs are moved only to Oracle-licensed clusters.
With host-based VM placement (VM-to-host tagging), you bind your VMs to individual hosts rather than clusters.
vCenter Server tags are implemented as key:value labels that enable operators to add meta-data to vCenter Server objects. In vCenter Server terminology, the key is the tag category and the value is the tag name. You can define many keys and values in vCenter Server, but choose a subset to be considered in the Business Intent pane of the Workload Optimization screen (Home -> Optimize Performance -> Workload Optimization).
- You are not permitted to employ both VM-to-cluster tagging and VM-to-host tagging in the same data center or custom data center - only one tagging method or the other. If you select host-based VM placement, any cluster tags are ignored.
- With host-based VM placement, only one category and one tag per VM is allowed per VM.
- A tagless VM can be sent to any host, even a tagged host.
- A host with multiple tags is treated as tagless.
- Even if all workloads are balanced, if there is also a tag violation, the system is by definition not optimized.
- The system does not consider any tags of storage - that is, datastores or datastore clusters.