--- title: "When *not* to use Invirtus VM Optimizer (Hint: with differencing disks!) + different space-saver way" url: "https://osherove.com/blog/2006/3/5/when-not-to-use-invirtus-vm-optimizer-hint-with-differencing.md" canonical: "https://osherove.com/blog/2006/3/5/when-not-to-use-invirtus-vm-optimizer-hint-with-differencing.html" published: "2006-03-05T01:35:00" updated: "2006-03-05T01:35:00" tags: [] author: "Roy Osherove" description: "When RTFM is not enough It was a fun experience downloading Invrituse's VM-Compacting solution , installing it, running it for a couple of hours on one of my VPC images, wait quite a bit, and only then realizing that…" usage: "Licensed under CC BY 4.0 — reuse, quote and adapt with attribution (Roy Osherove, link to the original page)." license: "https://creativecommons.org/licenses/by/4.0/" --- # When \*not\* to use Invirtus VM Optimizer (Hint: with differencing disks!) + different space-saver way By Roy Osherove March 5, 2006 **Historical article** · Originally published March 5, 2006; technical details may be outdated. **When RTFM is not enough** It was a fun experience downloading [Invrituse's VM-Compacting solution](http://www.invirtus.com/), installing it, running it for a couple of hours on one of my VPC images, wait quite a bit, and only then realizing that even though you can run the VM Compactor from within the running hosted operating system, the final step you need is an external one - using the Virtual PC Virtual Disk Wizard-Compact Disk, which **does not run on differencing disks**!. All that effort for nothing.  Invirtus would be very wise to put in on one of its top level headlines a big red line saying **don't use our product on differencing disks,** since you'll have to merge them with the parent disk before it can actually save you some space(which negates the whole idea of diff. disks..) . **So what \*can\* I do?** Luckily, there is another partial solution to this problem, which turned out to save me lots and lots of disk space: I put the parent images of my VPC into compressed NTFS folders. How much disk does it save? well, a standard 2GB sized image lots weight to around 300MB on disk. All by right clicking on the folder-> advanced->compressed folder check box. Don't do it on the actually diff. disk VPC, just on the parent disks, though, for perf reasons. **A workaround for differencing disks?** The Invirtus folk have [a different solution for using differencing disks](http://www.invirtus.com/blog/?p=8). a "workaround" if you will, which is weird but seems to work. basically, you rename your \*undo\* disk into a "vhd" extension file, and it works just like a differencing disk, but without the official title for it. What does that give you? not sure. haven't tried it. but perhaps it allows compacting it unlike the "real" diff. disks. Let me know if you have an answer.. --- ## About the author **Roy Osherove**: Senior Solutions Architect at AWS working on AI for production and AI-driven development; author of The Art of Unit Testing and Elastic Leadership, with about 20 years of consulting and training on unit testing, TDD, team leadership and continuous delivery. ### Sites - [RobotPaper](https://robotpaper.ai/): This blog: AI patterns and anti-patterns, AI and coding agents, and engineering leadership. - [osherove.com](https://osherove.com): Roy's personal site. Author of The Art of Unit Testing and Elastic Leadership; consulting and training on unit testing, TDD, team leadership and continuous delivery, plus about 20 years of blog posts. - [The Art of Unit Testing](https://www.artofunittesting.com): The Art of Unit Testing, 3rd Edition (Manning): readable, maintainable, trustworthy unit tests, plus TDD workshops in C#, JavaScript, Java and Kotlin. - [5whys.com](https://www.5whys.com): Roy's writing on software team leadership: self-organizing teams, surviving chaos, learning mode and the Elastic Leadership model. - [Pipeline Driven](https://pipelinedriven.org): Continuous delivery and DevOps practices: build patterns, pipeline-friendly testing, DevOps metrics and enterprise DevOps. - [Elastic Leadership](https://www.elasticleadership.com): Elastic Leadership, Roy's framework for software team leaders (survival, learning and self-organizing modes). ### Social - X: https://x.com/royosherove - LinkedIn: https://www.linkedin.com/in/osherove/ ### Contact - Contact form: https://forms.gle/jQSx5KoXvrVA1JCK7 ### License Licensed under CC BY 4.0 — reuse, quote and adapt with attribution (Roy Osherove, link to the original page). License: https://creativecommons.org/licenses/by/4.0/