One of the nice features about Hyper-V virtualized environments is the flexibility with which you can manage disk space. In one of my earlier blog posts, entitled “Onward to VHDX“, I talked about using virtual disks and the conversion of disks to the new VHDX format in Hyper-V 2012. But what can you do if you find that you need additional disk space for your VM after you have used it for a while? The Hyper-V Manager has just the tools to help, by allowing you to create and attach a new virtual disk to your running VM.  Just select your VM from the Hyper-V Manager’s list of VMs and you will see, in a panel on the right-hand-side, an item called “Settings…”. Clicking on it will open a pop-up which shows your VM’s current settings, and for certain types of hardware, will allow you to configure it while the VM is running. Note that some hardware changes will be grayed-out, requiring that the VM be shut down first. But for adding a disk, the really nice thing is that you do not have to reboot your VM if it can recognize the disk at run-time!

Let’s walk through an example with a Unitrends Free Backup for Hyper-V VM. After deployment, I have 80GB for my backups device, but I later find that it is not enough for my data protection needs, and I would like to add more. To add space, I go to Settings and then select “SCSI Controller”. I can then select “Add” for a Hard drive and follow the menus to add my disk.

If I already have a virtual disk, I can browse to it and attach it to my VM. If I do not, I can click on “New” and go through the Virtual Hard Disk Wizard and create my new disk.


UEB Hyperv1


If I already have a virtual disk, I can browse to it and attach it to my VM. If I do not, I can click on “New” and go through the Virtual Hard Disk Wizard and create my new disk.


UEB HyperV2


In this example, I am attaching a previously created VHDX called “new-disk-2” then click on “Apply” to attach it to my UEB VM.

Within the UEB VM itself, the underlying software recognizes the additional disk, but it is still unused, so I need to expand my backups storage to incorporate it. To do this, I can log into the UEB’s graphical user interface and go to the Storage subsystem under Settings.


UEB HyperV3

On the Storage screen, I find “Add Backup Storage” at the bottom and select it,  then “Expand your backup device across added disks” and finally  “Expand Storage” to include this new space in my backups storage pool.


UEB HyperV4


After the storage expansion finishes, I can use this additional space for my backups!


  1. I have been told that UEB isn’t approved for Hyper-V 2012 yet. My UEB locks up under Hyper-V 2012 partway through backups.

    One of the downsides of Hyper-V is that you can’t grow a VHD or VHDX file without first dismounting it from the VM or shutting down the VM. I find this to be a large limitation when dealing with VMs that may need to quickly grow a volume during production hours. It is for this reason that I often use iSCSI from within the VM to attach to my SAN. When I attach natively to a SAN from the VM, I can grow the volume without needing to take any of the resources offline.

    1. Thanks for your comment Kevin. UEB has been released on Windows Server 2012 with the Hyper-V Role but not Hyper-V 2012. And yes, expanding a VHD requires that the VM be shut down, which can be a significant limitation, depending on your environment. As described in the blog, UEB itself bypasses the limitation by allowing an additional VHD to be attached to the VM and the backups space expanded across the newly attached VHD while running.

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Unitrends increases uptime, productivity and confidence in a world in which IT professionals must do more with less. Unitrends leverages high-availability hardware and software engineering, cloud economics, enterprise power with consumer-grade design, and customer-obsessed support to natively provide all-in-one enterprise backup and continuity. The result is a “one throat to choke” set of offerings that allow customers to focus on their business rather than backup.