VMware Clusters
1. HA – High Availability Cluster
Whenever the ESXi host is down then automatically VM’s will migrate to another ESXi host and restart the VM’s.
There will be downtime expected for the VM’s.
It will install HA agent(Fault Domain Manager (FDM)) in ESXi host. FDM agent will run the election process.
Election process:
a. Maximum number of datastores – The host that mounts the greatest number of datastores has an advantage in the election.
b. Based upon the MOID value – The host with the lexically-highest Managed Object ID (MOID) is chosen(https://vcentername/mob/?moid=..)
Options:
Host Failure response and response for host isolation
Datastore with PDL – Permanent Device Loss (PDL): A datastore is shown as unavailable in the Storage view A storage adapter indicates the Operational State of the device as Lost
Datastore with APD – Communication All-Paths-Down (APD): A datastore is shown as unavailable in the Storage view.
VM Monitoring – VM monitoring resets individual VMs if their VMware tools heartbeats are not received within a set time. Application monitoring resets individual VMs if their in-guest heartbeats are not received within a set time.
Admission control – Admission control is a policy used by vSphere HA to ensure failover capacity within a cluster. Raising the number of potential host failures will increase the availability constraints and capacity reserved.
Host failures cluster tolerates
2. DRS – Distributed Resource Scheduler
It will balance the load accross the ESXi hosts and there will be no downtime.
Options:
a. Automation Level:
Full Automated – DRS automatically places virtual machines onto hosts at VM power-on, and virtual machines are automatically migrated from one host to another to optimize resource utilization.
Partial Automated – DRS automatically places virtual machines onto hosts at VM power-on. Migration recommendations need to be manually applied or ignored.
Manual – DRS generates both power-on placement recommendations, and migration recommendations for virtual machines. Recommendations need to be manually applied or ignored.
b. Migration Threshold:
Migration Threshold specifies how aggressively DRS recommends vMotions. Recommendations are generated automatically based on resources demanded by the virtual machines, resource allocation settings (reservations, limits, and shares) the resources provided by each host and the cost of migrating VMs. The more conservative the setting, the less frequent the vMotions.
c. Predictive DRS:
In addition to real-time metrics, DRS will respond to forecasted metrics provided by vRealize Operations Manager. Only forecasted metrics with high confidence will be considered by DRS to balance the cluster’s workloads prior to predicted utilization spikes and resource contention. You must also configure Predictive DRS in a version of vRealize Operations that supports this feature.
d. Virtual Machine Automation
Override for individual virtual machines can be set from the VM Overrides page.
Two types of rules:
1. Affinity — Keep virtual machines together
2. Inaffinity — Seperate virtual machines
3. Virtual machine to hosts
4. Virtual machines to virtual machines
EVC mode:
The EVC mode of a virtual machine determines the CPU and graphics features that a host must have in order for the virtual machine to migrate to that host and power on. The EVC mode of a virtual machine is independent from the EVC mode that you configure for the cluster in which the virtual machine runs.
