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?
In an effort to provide a more insightful user experience and to help understand how vSphere DRS works, we recently released a fling: DRS Dump Insight.
DRS Dump Insight is a service portal where users can upload drmdump files and it provides a summary of the DRS run, with a breakup of all the possible moves along with the changes in ESX hosts resource consumption before and after DRS run.
Users can get answers to questions like:
Why did DRS make a certain recommendation?
Why is DRS not making any recommendations to balance my cluster?
What recommendations did DRS drop due to cost/benefit analysis?
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.
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:
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.
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.
VMware vSphere Distributed Resource Scheduler (DRS) is responsible for placement of Virtual Machines and balancing of resources in a cluster. The key driver for DRS is VM/Application happiness, and it achieves this by effective VM placement and efficient load balancing. We have a new white paper, which tries to explain how DRS works in basic scenarios and how it can be tuned to behave differently for specific scenarios.
The white paper talks about the factors that influence DRS decisions and provides some useful insights into different parameters that can be tuned in specific scenarios to make DRS more effective. It also explains how to monitor DRS to better understand its behavior.
It covers DRS behavior in specific scenarios with some case studies. Some of these studies are around
VM Consumed vs. Active Memory – How it impacts DRS behavior.
Impact of VM overrides on cluster balance.
Prerequisite moves during initial placement.
Using shares to prioritize cluster resources.
The paper provides knowledge about the factors that affect DRS behavior and helps understand how DRS does what it does. This knowledge, along with monitoring and troubleshooting tips, including real case studies, will help tune DRS clusters for optimum performance.
Mystery revealed, DRS for VMware vSphere is no more a black box! DRS Doctor will tell you all you need to know about your DRS clusters.
Our latest fling, DRS Doctor, will monitor your DRS clusters for virtual machine and host resource usage data, DRS-recommended migrations, and the reason behind each migration. It also monitors all the cluster-related events, tasks, and cluster balance, and logs all this information into a plain text log file that anyone can read.
Read this blog for more information on how DRS Doctor can monitor and diagnose your clusters.