Resizing your zvol in FreeNAS and Windows
Upon needing to expand your zvol for additional storage, there are only a few simple steps needed to achieve this. Doing this will not delete the data already residing on this zvol.
The first step is to go to your FreeNAS web interface, and click on the Storage tab. Click on the zvol to see three buttons at the bottom of the page. Shown below is this exact situation, with a 1TB zvol.
Click on the middle wrench button to Edit the zvol to a 2TB zvol by changing the number in the Size text box.
When done, click edit ZFS Volume. On your windows computer, run Computer Management as the administrator. From there go to Storage –> Disk Management in the list on the left hand side. The page should load up and you should see your zvol as one of the Disks listed like Disk 2 shown below.
After updating the zvol size in FreeNAS, click on More Actions and then Refresh in the right hand side Actions bar to get the new allocated storage space to expand to. Doing so will result in the following.
Right click on the Primary partition (zvol) to drop down a list and click on Extend Volume. A window will open for the Extend Volume Wizard, click Next> twice and then Finish assuming you’d like to add all of the extra space you’ve specified in FreeNAS.
Going into This PC, and then zVol (E:), right clicking and then Properties, shown below the zvol is now extended to 2TB, along with FreeNAS showing the used amount of space.