14th September 2017

Objective 5.2 – Configure vSphere DRS and Storage DRS Clusters

Wrapping up section 5, we have Objective 5.2 – Configure vSphere DRS and Storage DRS Clusters

As always this article is linked to from the main VCP6.5-DCV Blueprint.

Happy Revision

Simon

Add/remove Host DRS Group

Create a Host DRS group

Browse to the cluster in the vSphere Web Client navigator.
Click the Configure tab.
Under Configuration, select VM/Host Groups and click Add.
In the Create VM/Host Group dialog box, type a name for the group.
Select Host Group from the Type drop down box and click Add.
Click the check box next to a host to add it. Continue this process until all desired hosts have been added.
Click OK.

Add/remove virtual machine DRS Group

Create a VM DRS Group

Browse to the cluster in the vSphere Web Client navigator.
Click the Configure tab.
Under Configuration, select VM/Host Groups and click Add.
In the Create VM/Host Group dialog box, type a name for the group.
Select VM Group from the Type drop down box and click Add.
Click the check box next to a virtual machine to add it. Continue this process until all desired virtual machines have been added.
Click OK.

Manage DRS affinity/anti-affinity rules

Browse to the cluster in the vSphere Web Client navigator.
Click the Configure tab.
Under Configuration, click VM/Host Rules.
Click Add.
In the Create VM/Host Rule dialog box, type a name for the rule.
From the Type drop-down menu, select either Keep Virtual Machines Together or Separate Virtual Machines.
Click Add.
Select at least two virtual machines to which the rule will apply and click OK.
Click OK.

Configure the proper DRS automation level based on a set of business requirements

Automation levels are described as follows.

Manual

Placement and migration recommendations are displayed, but do not run until you manually apply the recommendation.

Fully Automated

Placement and migration recommendations run automatically.

Partially Automated

Initial placement is performed automatically. Migration recommendations are displayed, but do not run.

Disabled

vCenter Server does not migrate the virtual machine or provide migration recommendations for it.

To change the automation level on a per VM basis

Browse to the cluster in the vSphere Web Client navigator.
Click the Configure tab and click Services.
Under Services, select vSphere DRS and click Edit. Expand DRS Automation.
Select the Enable individual virtual machine automation levels check box.
To temporarily disable any individual virtual machine overrides, deselect the Enable individual virtual machine automation levels check box.

Virtual machine settings are restored when the check box is selected again.

To temporarily suspend all vMotion activity in a cluster, put the cluster in manual mode and deselect the Enable individual virtual machine automation levels check box.
Select one or more virtual machines.
Click the Automation Level column and select an automation level from the drop-down menu.

Click OK.

Explain how DRS affinity rules effect virtual machine placement

You can control the placement of virtual machines on hosts within a cluster by using affinity rules.

You can create two types of rules.

Used to specify affinity or anti-affinity between a group of virtual machines and a group of hosts. An affinity rule specifies that the members of a selected virtual machine DRS group can or must run on the members of a specific host DRS group. An anti-affinity rule specifies that the members of a selected virtual machine DRS group cannot run on the members of a specific host DRS group.
Used to specify affinity or anti-affinity between individual virtual machines. A rule specifying affinity causes DRS to try to keep the specified virtual machines together on the same host, for example, for performance reasons. With an anti-affinity rule, DRS tries to keep the specified virtual machines apart, for example, so that when a problem occurs with one host, you do not lose both virtual machines.

When you add or edit an affinity rule, and the cluster’s current state is in violation of the rule, the system continues to operate and tries to correct the violation. For manual and partially automated DRS clusters, migration recommendations based on rule fulfillment and load balancing are presented for approval. You are not required to fulfill the rules, but the corresponding recommendations remain until the rules are fulfilled.

To check whether any enabled affinity rules are being violated and cannot be corrected by DRS, select the cluster’s DRS tab and click Faults. Any rule currently being violated has a corresponding fault on this page. Read the fault to determine why DRS is not able to satisfy the particular rule. Rules violations also produce a log event.

Understand Network DRS

Traditionally, DRS has always considered the compute resource (CPU and memory) utilizations of hosts and VMs for balancing load across hosts and placing VMs during power-on. This generally works well because in many cases, CPU and memory are the most important resources needed for good application performance. However, since network availability is not considered in this approach, sometimes this results in placing or migrating a VM to a host which is already network saturated. This might have some performance impact on the application if it happens to be network sensitive.

DRS is network-aware in vSphere 6.5, so it now considers the network utilization of host and network usage requirements of VMs during initial placement and load balancing. This makes DRS load balancing and initial placement of VMs more effective.

During initial placement and load balancing, DRS first comes up with the list of best possible hosts to run a VM based on compute resources and then uses some heuristics to decide the final host based on VM and host network utilizations. This makes sure the VM gets the network resources it needs along with the compute resources.

The goal of network-aware DRS in vSphere 6.5 is only to make sure the host has sufficient network resources available along with compute resources required by the VM. So, unlike regular DRS, which balances the CPU and memory load, network-aware DRS does not balance the network load in the cluster, which means it will not trigger a vMotion when there is network load imbalance.

DRS does initial placement in two steps:

It compiles the list of possible hosts based on cluster constraints and compute resource availability and ranks them.
Then, from the list of hosts, it picks the host with the best rank and best network resource availability

Differentiate load balancing policies

During a load balancing run, DRS

First generates the list of possible migration proposals.
Then eliminates the proposals whose destination hosts are network saturated.
From the remaining list of proposals, recommends the one with the maximum balance improvement in terms of compute resources and that also contributes to network resource availability on the source host, in case the source host is network saturated.

Host Network Saturation Threshold

As mentioned earlier, DRS will avoid a network loaded host during load balancing decisions, only if its network utilization is beyond a certain threshold. This threshold is set to 80% by default. So, unless the host network utilization is above 80%, DRS considers the host to be a good candidate in terms of network resource availability.

If a host’s network utilization is at or above the saturation threshold, DRS considers it to be network saturated. If all the hosts in the cluster are network saturated, DRS will prefer not to migrate VMs with network load, since migrating network loaded VMs to an already network saturated host would result in further degradation of VM performance. When DRS cannot migrate VMs due to this behavior, this can sometimes result in an imbalanced cluster.

Monitoring Host Network Utilization

Starting in vSphere 6.5, you can monitor the host network load distribution under the DRS monitoring tab in the vSphere Web Client.

The network utilization percentage of a host is the average capacity that is being utilized across all the physical NICs (pNICs) on that host. For example, if a host has three pNICs, one of them is 90% utilized and the other two are 0% utilized, then the network utilization of the host is considered to be 30%.

Describe Predictive DRS

vSphere Predictive DRS can proactively load balance a vCenter Server cluster to accommodate predictable patterns in the cluster workload.

Whereas DRS performs load balancing of hosts within a cluster by considering the last five minutes of virtual machine demand, Predictive DRS acts based on data provided to it by vRealize Operations Manager. vRealize Operations Manager monitors virtual machines running in a vCenter Server, analyzes longer-term historical data, and provides forecast data about predictable patterns of resource usage to Predictive DRS. Predictive DRS moves to balance resource usage among virtual machines based on these predictable patterns