Welcome!

Microsoft Cloud Authors: Nick Basinger, Kevin Benedict, Pat Romanski, Liz McMillan, Lori MacVittie

Blog Feed Post

Your choice in .VHD files, and what it implies (So many questions. So little time. Part 36)

Jeanne asked two questions at our TechNet Event a couple of weeks ago:

Evaluate the Private Cloud

So.. in question #1 you’re asking about the implications of using one particular .VHD (virtual hard disk) disk type; Fixed, Differencing, or Dynamic.  To answer that question, first let me take a minute to describe what these types are.  I’ll point to some benefits and weaknesses, and then I’ll point you to some documentation on what the performance impacts are.

First of all you should understand that when you create a VHD file you have three choices.  Two of these choices concern the difference between what the virtual machine or file system thinks it has when compared the actual file of the disk, and one has to do with a linked relationship between disks.

Fixed: This is a disk that, to the file system using it, believes it is a certain size.. and that size matches the actual size of the .VHD file.  So if I create a virtual disk for a virtual machine that believes it has 40GB on its C: drive, the .VHD file is approximately 40GB in size.

Dynamic: This is in contrast to the Fixed-type disk.  In this case, the operating system or file system sees 40GB in the disk, but the size of the .VHD file starts small and grows dynamically as more information is added to it; potentially growing to the full capacity eventually.

Differencing: This is a parent/child relationship.  Or a grandparent/parent/child relationship.  Or a great-grandparent/grandparent/parent/child relatio…

“Get on with it!”

Sorry.  The idea is that you have a .VHD that is a basis, or starting point of content for a new child disk.  Let’s say the .VHD that is going to be the parent is a fully installed and sysprep’d copy of an operating system.  So it’s ready for duplication.  Then you create differencing disks that refer to the common parent.  Those new machines based on the parent will all have the contents of the parent, plus whatever changes gets written in the child; or in the lowest-most disk in the chain of differencing disks.  IMPORTANT: Once you have based one or more children off of a parent disk, the parent .VHD file must never be modified.  If it is, any disk that they are based on becomes invalid and won’t work. 

“What’s the benefit, then, of differencing disks?”

Mainly there are two benefits:

  1. It’s potentially a quick way to create new machines off of a pre-installed, up-to-date operating system installation.  For example, in my 3-part screencast series on the System Center 2012 Unified Installer, I created all 8 of my virtual machines from the same parent disk.
  2. It’s a huge savings in space.  Differencing disks are dynamic disks that start out small and grows with any changes or additions to the system using it, so it’s easier to fit many more virtual machines in limited space.  In my case, the main place I like to put my virtual machines is a 160GB SSD.  I put my parent on a separate drive, and this way I can fit more new machines on that SSD. 

So what are the performance implications of these options, Kevin?” 

Of course, the more disk operations that are required, the more performance can be degraded.  The .VHD file option with the smallest impact in performance is a Fixed size disk.  (I mention .VHD File option because you do have the ability to run a virtual machine on a “Pass-thru” disk – which is pointing to an actual file or storage system location for the virtual machine to use as its disks.  That is even more efficient than .VHD files in terms of performance; but you lose the big benefits of flexibility and transportability that a virtual machine running off of file system objects gives you).  Next would be Dynamic Disks.  Operations to grow the disk add overhead when it’s required.  The same can be said for differencing disks, because as I mentioned above, your child disk is essentially a dynamic disk.  Changes that would have otherwise been written to the parent are being committed in the child, and that child .VHD file will grow as needed.

“Where can I go to get more detailed information?  Is there anything like, say, a ‘Windows Server 2008 R2 Hyper-V Virtual Hard Disk Performance Whitepaper’?”

As a matter of fact, there is exactly something like that:  ‘Windows Server 2008 R2 Hyper-V Virtual Hard Disk Performance Whitepaper’  Enjoy.

---

In question #2, you are looking for a small-business equivalent of System Center 2012’s Service Manager component; something along the lines of Microsoft’s System Center Essentials, but with some (or all) of the functionality of Service Manager. 

I’m afraid that doesn’t exist.  At least not from Microsoft.  What happens in the future I don’t know and can’t speculate on, but for now, I don’t know of a product for small-to-midsized businesses that does what Service Manager does.

In case you’re interested in System Center Essentials, check out these resources:

---

I hope that helps.  Let me know.

Read the original blog entry...

More Stories By Kevin Remde

Kevin is an engaging and highly sought-after speaker and webcaster who has landed several times on Microsoft's top 10 webcast list, and has delivered many top-scoring TechNet events and webcasts. In his past outside of Microsoft, Kevin has held positions such as software engineer, information systems professional, and information systems manager. He loves sharing helpful new solutions and technologies with his IT professional peers.

A prolific blogger, Kevin shares his thoughts, ideas and tips on his “Full of I.T.” blog (http://aka.ms/FullOfIT). He also contributes to and moderates the TechNet Forum IT Manager discussion (http://aka.ms/ITManager), and presents live TechNet Events throughout the central U.S. (http://www.technetevents.com). When he's not busy learning or blogging about new technologies, Kevin enjoys digital photography and videography, and sings in a band. (Q: Midlife crisis? A: More cowbell!) He continues to challenge his TechNet Event audiences to sing Karaoke with him.

IoT & Smart Cities Stories
Never mind that we might not know what the future holds for cryptocurrencies and how much values will fluctuate or even how the process of mining a coin could cost as much as the value of the coin itself - cryptocurrency mining is a hot industry and shows no signs of slowing down. However, energy consumption to mine cryptocurrency is one of the biggest issues facing this industry. Burning huge amounts of electricity isn't incidental to cryptocurrency, it's basically embedded in the core of "mini...
Every organization is facing their own Digital Transformation as they attempt to stay ahead of the competition, or worse, just keep up. Each new opportunity, whether embracing machine learning, IoT, or a cloud migration, seems to bring new development, deployment, and management models. The results are more diverse and federated computing models than any time in our history.
At CloudEXPO Silicon Valley, June 24-26, 2019, Digital Transformation (DX) is a major focus with expanded DevOpsSUMMIT and FinTechEXPO programs within the DXWorldEXPO agenda. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of business. Only 12% still survive. Similar percentages are found throug...
Japan DX Pavilion at @CloudEXPO Silicon Valley
The graph represents a network of 1,329 Twitter users whose recent tweets contained "#DevOps", or who were replied to or mentioned in those tweets, taken from a data set limited to a maximum of 18,000 tweets. The network was obtained from Twitter on Thursday, 10 January 2019 at 23:50 UTC. The tweets in the network were tweeted over the 7-hour, 6-minute period from Thursday, 10 January 2019 at 16:29 UTC to Thursday, 10 January 2019 at 23:36 UTC. Additional tweets that were mentioned in this...
In his general session at 19th Cloud Expo, Manish Dixit, VP of Product and Engineering at Dice, discussed how Dice leverages data insights and tools to help both tech professionals and recruiters better understand how skills relate to each other and which skills are in high demand using interactive visualizations and salary indicator tools to maximize earning potential. Manish Dixit is VP of Product and Engineering at Dice. As the leader of the Product, Engineering and Data Sciences team at D...
At CloudEXPO Silicon Valley, June 24-26, 2019, Digital Transformation (DX) is a major focus with expanded DevOpsSUMMIT and FinTechEXPO programs within the DXWorldEXPO agenda. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of business. Only 12% still survive. Similar percentages are found throug...
Where many organizations get into trouble, however, is that they try to have a broad and deep knowledge in each of these areas. This is a huge blow to an organization's productivity. By automating or outsourcing some of these pieces, such as databases, infrastructure, and networks, your team can instead focus on development, testing, and deployment. Further, organizations that focus their attention on these areas can eventually move to a test-driven development structure that condenses several l...
The term "digital transformation" (DX) is being used by everyone for just about any company initiative that involves technology, the web, ecommerce, software, or even customer experience. While the term has certainly turned into a buzzword with a lot of hype, the transition to a more connected, digital world is real and comes with real challenges. In his opening keynote, Four Essentials To Become DX Hero Status Now, Jonathan Hoppe, Co-Founder and CTO of Total Uptime Technologies, shared that ...
Over the course of two days, in addition to insightful conversations and presentations delving into the industry's current pressing challenges, there was considerable buzz about digital transformation and how it is enabling global enterprises to accelerate business growth. Blockchain has been a term that people hear but don't quite understand. The most common myths about blockchain include the assumption that it is private, or that there is only one blockchain, and the idea that blockchain is...