Overview of VMWare DRS

Overview of VMWare DRS - Distributed Resource Scheduler

Written by Damian Murdoch   

Tuesday, 27 June 2006

Overview of VMWare DRS - Distributed Resource Scheduler

VMWare DRS is a new technology that will automatically move Virtual Machines around your cluster of ESX 3.0 servers to their optimal location based on complex rule sets and user defined resource pools by utilising VMotion technology. This article will provide an overview of the technology and allow you to make an informed decision on the benefits DRS can provide to you and your business.

VMWare DRS is one of two enabling technologies from VMware in Virtual Infrastructure 3 that removes hardware dependancies and allows hardware to be assigned as a pool of resources to virtual machines. The other one of course is VMWare HA or High Availability and we will have another article on that one soon. It allows businesses to leverage their hardware to maximum possible utilisation, allocate high priority applications preference to hardware, and dynamically allocate hardware from the user defineable resource pool. You can also reduce downtime by letting DRS automatically reassign machines to other resources when a host is put in maintenance mode. New capacity can be added to the resource pool on the fly and the virtual machines can then take immediate advantage of the new hardware resources!

There are some basic configurable options in VMWare DRS. These include configurable automation levels of Manual, Partial and Full. Manual only recommends the inital startup host and the migrations, Partial will choose the startup host and recommend the migrations, while Automatic will automate the startup host and migrations. The old resource controls are still there from previous versions, with shares for weighting and min/max assignments.

Resource Pools

Resource pools appear as objects in the Virtual Center directory, they can contain parent pools, child pools and virtual machines. They also have access permissions and resource options that include max/min and shares. A resource pool spans host resources, and virtual machines in a resource pool can use resources from the resource pool they exist in. Resource pools can be nested within each other though they can provide isolation as well. As mentioned before, one of the big bonuses with Resouce Pools is that you can dynamically allocate new resources to the pools and let the VM's immediately take advantage of the new resources. Keep in mind that by default, the default pool contains all cluster resources.

You can delegate permissions to manage pool resources. There are three levels of delegation, they include :

• The Cluster Administrator - The cluster administrator combines the resources from the cluster and then can provide large resource allocations to the next level of administrator if needed.
• Pool Administrator - The pool administrator can then divide the large resource allocation they have been given by the cluster administrator into smaller pools for the end user. The pool administrator would normally be responsible for management of department or business unit resources.
• The End User - The end user is restricted to view their own personal pool assignments and can allocate resources from their pools to virtual machines. Normally this person would be an application administrator or the business owner of an application.

How does DRS figure out where to put the virtual machines ?

While VMWare would never release the metrics or the algorithms they use to figure out the dynamic allocations, I can tell you what we do know about this process. There are some constraints associated with DRS, and the big one is the standard VMotion constraints. If you cannot VMotion then you cannot use DRS, maybe you have two seperate VMotion pools ? Then you are going to also have to arrange your resource pools around that.

DRS takes into account processor affinity which include affinity rules and anti-affinity rules. The anti-affinity rules take into account high availability and clustering while the affinity rules take into account performance. The dynamic balancing component of DRS (read: Automatic VMotion) is adjusted based on the Virtual Machines resource requirement at any given time. The DRS balancing component is re-evaluated every few minutes based on millisecond performance evaluation over that period of time across the whole resource pool. A balancing re-evaluation is also done when the pool settings change, this includes resource entitlements or VM pool assignments. If the imbalance in the resource pool is high then the balancing component will be more agressive than if the imbalance is low.

The rules also suggest that virtual machines will be allocated resources fairly, based on the pool and virtual machine resource settings.  Possible VMotions are evaluated based on the final effect of the migration on the destination host and the migration cost.

Sounds great! Where can I get it and how much ?

Vmware Dynamic Resource Scheduler list price is $2000 US, but speak to your reseller it should be able to be bought for less than that. Though if you have the Enterprise Edition of VI3 then you get it included in your package!

Thats it for this one everyone. And on another note, why don't you register and say hello in the forums!

Last Updated ( Wednesday, 28 June 2006 )

 

ZT: