Microsoft details upcoming Hyper-V Dynamic Memory feature

Posted by Staff   |   Monday, March 22nd, 2010   |  

microsoft logo

There’s a lot of interest around the just announced Dynamic Memory feature that will be included in Hyper-V as soon as Microsoft release the Service Pack 1 for Windows Server 2008 R2 (rumored to arrive no earlier than Q4 2010).

For a lot of time Microsoft downplayed the VMware’s memory overcommitment techniques, suggesting that they are the solution for every problem and that even the competitor recommends to not use them. Now this Dynamic Memory, which was originally planned for a 2009 release, seems exactly a memory overcommitment feature.

James O’Neill, IT Pro Evangelist at Microsoft, shares some concrete details about the feature for the first time, trying to explain why Dynamic Memory is not about overcommit memory: 

…CPU is naturally dynamic: the CPU switches workload to another; we can reserve a quantity of CPU for a VM and or cap the amount it gets and if total CPU demand exceeds supply, weightings mean the shares granted to each VM do not need to be equal. Network is the same: packets go in or out – the NIC is works for one task at a time but multiple tasks are easily multiplexed through a single physical Network interface. Storage is different – because stuff is stored whether it is actively being processed or not, so commitment of disk space is long term. We don’t have to allocate all the disk a VM might use when we create the VM: instead of a fixed-size disk, dynamic disks can grow as needed – the sum of maximum disk sizes can be greater than disk capacity of the host, but at any given time we can’t use more disk than there is present. Now we’re applying that to memory…

VMs either have fixed size memory or a minimum , maximum and weight. So we don’t need to commit memory based on the peaks in load in the VM – dynamic memory will monitor demand for memory and use the hot-add capabilities of modern OSes to  increase memory. Eventually all the memory will be committed and since you can’t hot unplug memory we have a component to take memory out of use in one VM so that it can be given to another – and Hyper-V will take memory from the VMs which need it least. Dynamic memory won’t be supported on every possible operating system…

By de-allocating memory in VMs Hyper-V ensures the total allocated remains below the total present: when a VM can’t receive any more memory the OS in it will decide which caches should be abandoned, and which pages they should swap to disk. Hyper-V never swaps VM’s memory to disk.  You can have a design which over-allocates, and swaps when over-committed (and uses page sharing to allow some over-allocation before reaching the point of over-committing) or one which doesn’t swap and so doesn’t need page sharing to reduce swapping – but can’t over-allocate either…

So Dynamic Memory uses the memory ballooning technique. Problem is that multiple virtualization players, not just VMware, seem to agree that ballooning can be considered a form of memory overcommitment.
Oracle for example.

It may be just a matter of terminology, but this kind of things confuses the customers that, at the end of the day, need comparison terms to evaluate competing solutions.
The choice to not adopt the same terminology that the rest of the industry is using is not going to avoid comparison, it will just slow it down, leaving room for misunderstandings and misleading statements.


blog comments powered by Disqus Newest articles
Release: VMware vRealize Log Insight 4.5

June 13th, 2017

Log Insight is a log aggregation, management and analysis tool, that VMware first introduced in 2013 and considered a competitor of Splunk.
Yesterday VMware announced the release of version 4.5, available for…

Release: VMware vRealize Automation 7.3

June 6th, 2017

Today VMware announced the latest release of its cloud management platform vRealize Automation, former vCloud Automation Center.
VMware vRealize Automation 7.3 release notes can be found at this link.


Paper: Introducing the NSX-T Platform

February 9th, 2017

“We see greater potential strategic opportunity in NSX over the next decade than our franchise product vSphere has had for the past decade.”
said VMware’s CEO Pat Gelsinger talking about…

Paper: VMware vSphere Virtual Machine Encryption Performance

November 22nd, 2016

Encryption of virtual machines is something that has been requested for years by the security community. VMware continued to postpone its implementation due to the negative operational impact that many…

Quest Software leaves Dell

November 1st, 2016

In September 2012 Dell announced to have completed the acquisition of Quest Software, a Californian company with an history in systems management, security, business intelligence and, falling back in our…

Citrix announces Q3 2016 results

October 21st, 2016

Citrix announced its financial results for third quarter 2016.
The revenues for the second quarter were $841 million for an increase of 3% compared to Q3 2015.
Net income was $132…

Release: VMware vSphere 6.5 & Virtual SAN 6.5

October 19th, 2016

2016 edition of VMworld US has been quite turbulent, on the other hand during VMworld Europe, happening these days in Barcelona, the company announced a few more products for the…

Release: VMware vRealize Log Insight 4.0

October 18th, 2016

Log Insight is a log aggregation, management and analisys tool, that VMware first introduced in 2013 and now is usually compared with Splunk.
Yesterday VMware announced Log Insight’s new major…

Release: Windows Server 2016 with support for Window Server & Hyper-V containers

October 13th, 2016

Yesterday Microsoft announced the general availability of Windows Server 2016 which the company defines as a cloud-ready OS.
Beside fancy definitions, one of the most relevant perks of this release…

Release: Oracle VM 3.4.2

September 22nd, 2016

During Oracle OpenWorld 2016 the company released version 3.4.2 of its enterprise virtualization solution.
Oracle VM is available for both x86 and SPARC based processor architectures and uses the Xen hypervisor…

VMworld US 2016 Wrap-up

September 1st, 2016

Today was the last day of VMware’s flagship conference VMworld in Las Vegas, an highly controversial edition which left a good chunk of the audience disoriented if not properly disappointed….

Gartner releases its Magic Quadrant for Cloud Infrastructure as a Service for 2016

August 11th, 2016

Last week Gartner updated its Magic Quadrant for Cloud Infrastructure as a Service (IaaS) for the year 2016. The Magic Quadrant for the year 2015 was released in May last year…

Release: Ansible Tower 3 by Red Hat

August 2nd, 2016

Ansible is one of the four main players in the automation market, younger then the well known Chef and Puppet, has been launched in 2013 in Durham, N.C. and acquired…

IBM announces earnings for Q2 2016

July 19th, 2016

Yesterday IBM announced its results for Q2 2016.

If we compare with the same quarter in 2015 earnings per share, from continuing operations, decreased 22%. Net income, from continuing operations,…

Monthly Archive