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Author Archives: Sai Inabattini

DRS Entitlement Viewer

Ever wondered how DRS distributes resources to VMs? How much resources your VMs are entitled to? How reservations, limits, and shares (RLS) affect your VMs’ resource availability? Our new fling, DRS Entitlement Viewer, is the answer.

DRS Entitlement Viewer is installed as a plugin to the vSphere Client. It is currently only supported for the HTML5-based vSphere Client. Once installed, it gives the hierarchical view of vCenter DRS cluster inventory with entitled CPU and memory resources for each resource pool and VM in the cluster.

Entitled resources can change with VMs’ resource demand and with the VM’s and resource pool’s RLS settings. So, users can get the current entitlements based on the VMs’ current demands and RLS settings of the VMs and resource pools.

DRS Entitlement Viewer also provides three different what-if scenarios:

Changing RLS settings of a VM and/or resource pool
What-if all the VMs’ resource demand is at 100%
Both 1 and 2 happen together

Users can pick one of the three scenarios and can get new entitlements without actually changing RLS settings on the cluster.

Finally, DRS Entitlement Viewer also provides an option to export the new RLS values from a what-if scenario as a vSphere PowerCLI command that customers can execute against their vCenter to apply the new settings.

What-If? Resource Management with vSphere DRS

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vSphere Distributed Resource Scheduler (DRS) provides a simple and easy way to manage your cluster resources. DRS works well, out of the box for most vSphere installations.

For cases where more flexibility is desired in how the cluster is managed, DRS provides many options in the form of cluster rules, settings and advanced options.

Often the impact of using rules in a DRS cluster is not very well understood. The settings and advanced options are not very well documented. Imagine if it was possible to play around with rules in your cluster before actually applying them, or changing the DRS migration threshold in your cluster without changing the setting in your live cluster – and yet, be able to visualize the impact of those actions in your cluster?

Introducing – DRS Dump Insight – to help with simple queries regarding DRS behavior, like the following.

What if I dropped all the affinity rules in my cluster?
What if I set cluster advanced option “AggressiveCPUActive”?
What if I changed the DRS migration threshold from 3 to 5?

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Introducing DRS DumpInsight

DRS Lens – A new UI dashboard for DRS

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DRS Lens provides an alternative UI for a DRS enabled cluster. It gives a simple, yet powerful interface to monitor the cluster real time and provide useful analyses to the users. The UI is comprised of different dashboards in the form of tabs for each cluster being monitored.

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DRS Cluster Resource Management with Reservation and Shares

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Resource management in vSphere is very robust and sophisticated. It provides settings like reservation, limits and shares (a.k.a. RLS), which can be applied on virtual machines (VMs) and resource pools. These settings can be used as knobs to isolate resources, prioritize them, or to guarantee availability of resources to VMs in a cluster. Our customers have often asked about how these settings impact availability of resources for a VM.

Recently we published a white paper based on our study, to explain how reservation and shares can impact resource availability for VMs when they are applied on VMs versus when they are applied on resource pools. In the paper, we also share some general guidelines on when and how these settings can be used.

vSphere 6.5 DRS Performance – A new white-paper

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VMware recently announced the general availability of vSphere 6.5. Among the many new features in this release are some DRS specific ones like predictive DRS, and network-aware DRS. In vSphere 6.5, DRS also comes with a host of performance improvements like the all-new VM initial placement and the faster and more effective maintenance mode operation.

If you want to learn more about them, we published a new white-paper on the new features and performance improvements of DRS in vSphere 6.5. Here are some highlights from the paper:

Expandable Reservation for Resource Pools

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One of the questions I was often asked about resource pools (RP) is ‘Expandable reservation’. What is expandable reservation, and why should I care about it? Although it sounds intuitive, it can be easily misunderstood.

To put it simply, a resource pool with ‘expandable reservation’ can expand its reservation by asking more resources from its parent .

The need to expand reservation comes from the increase in reservation demand of its child objects (VMs or resource pools). If the parent resource pool is short of resources, then the parent expands it reservation asking resources from the grand parent.

Let us try to understand this with a simple example. Consider the following RP hierarchy. If RP-4 has to expand its reservation, it requests resources from its parent RP-3 and if RP-3 has to expand resources it eventually requests Root-RP.

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Latency Sensitive VMs and vSphere DRS

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Some applications are inherently highly latency sensitive, and cannot afford long vMotion times. VMs running such applications are termed as being ‘Latency Sensitive’. These VMs consume resources very actively, so vMotion of such VMs is often a slow process. Such VMs require special care during cluster load balancing, due to their latency sensitivity.

You can tag a VM as latency sensitive, by setting the VM option through the vSphere web client as shown below (VM → Edit Settings → VM Options → Advanced)

By default, the latency sensitivity value of a VM is set to ‘normal’. Changing it to ‘high’ will make the VM ‘Latency Sensitive’. There are other levels like ‘medium’ and ‘low’ which are experimental right now. Once the value is set to high, 100% of the VM configured memory should be reserved. It is also recommended to reserve 100% of its CPU. This white paper talks more about the VM latency sensitivity feature in vSphere.

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