Capturing Differencing Disks

A differencing disk is a Virtual Hard Disk (VHD) that contains changes made to another VHD. The purpose of a differencing disk is to maintain information about changes made, so that they can be revered if needed. Captured differencing disks are stored on the Virtual Machine (VM) profile.

Capturing differencing disks allows you to permanently persist changes you've made in your Virtual Machines. The changes will be present for all users that launch this lab in the future. This feature is only available to lab developers and shouldn't be mistaken as a way to temporarily save your lab. If you simply want to save your lab so you can resume it later, please use the Save and Close Lab option in the Exit menu.

Best Practices for Capturing Disks

Reduce Capture Time and Disk Size

• Begin working with a VM that has no differencing disks captured already.
• Make a checklist of all configuration items you need to accomplish, from installing the OS, to configuring all the software the lab will need to support.
• Capture a complete configuration. Capturing a diff after every small change made in the lab is inefficient (unless the only change needed is a small one).

• Don't leave the VM running for hours, and then capturing. This will increase the size of the disk and could affect VM performance.

Virtual Machine Optimization

• Ensure the base VM is optimized, to reduce the size of captured differencing disks. This can be done by completing as much configuration and/or changes as possible, before capturing the first differencing disk.

• Optimizing your VM using Virtual Desktop Infrastructure (VDI) principles, guidelines, and tools will help improve the performance of your VM. There are many tools available, to assist in optimization. The most common VDI tools are:

  • Citrix Optimizer

  • ESX OS Optimization Tool

• After installing the operating system and completing software configurations, you should consider using a second differencing disk capture for any files needed in the lab. If you need to add or remove these files later, you will be making changes to a much smaller disk. Additionally, this allows you to use the disk in different lab profiles that may need to use those lab files.

• Manually shut down the VM before capturing a differencing disk.

  • When capturing a differencing disk, part of the automated process shuts down the VM before capturing the differencing disk. In some scenarios, a processes in Windows (such as Windows updates) could prevent a graceful shutdown of the VM, and cause the disk capture to time out.

Differencing Disk Capture

To capture a differencing disk:

1. Navigate to the lab profile that uses the VM you want to capture a differencing disk for.
2. Launch the lab
3. Log in to the VM and make any changes that you would like to persist for each lab instance of the lab. For example, software installations and/or configurations.
4. In the running lab, select the Hamburger menu in the top right and choose the Save option.

1. A dialog window will appear with two development options:

   • Commit my changes and create a new lab profile.: creates a new lab profile with an option to create new virtual machine(s), as well as an option to copy the instructions to the new lab profile.

   • Commit my changes and update this lab profile.: updates the VMs used in the lab with changes saved during the differencing disk capture.

   

2. After selecting an option, fill out all fields as needed ensuring that all disks that have changes are checked and then select Next.

3. The differencing disk will now begin to capture.

Manual Captures

• In the rare event of errors during the differencing disk save process it is possible for us to capture the disks manually to update the lab data on the profile, should this happen please reach out to us via our normal Customer Support forms by opening a support ticket.