New to Parallels Desktop? Learn How to Handle “Out of Space” Warnings.


This post is part of a series to assist new users with Parallels Desktop.

“How can I be out of space? My Mac has more than 100GB of free space!”

Yes, it is possible for a Parallels® Desktop for Mac user to receive “Out of Space” warnings, even when the Mac has 100s of gigabytes of free space. In this blog post, I will explain why this can happen, and how to handle it.

When you install a Windows virtual machine (VM) on your Mac, you will have two separate operating systems, each of which can send you an “Out of Space” warning concerning their respective disk storage systems. Remember that Windows doesn’t “know” that it is running on a Mac, and the macOS doesn’t “know” that it is sharing the Mac with Windows.

Virtual Hard Disks (VHD)

Before I can explain why you are receiving an “Out of Space” warning, I need to first explain more about the hard drive that Windows thinks it is stored on. From the point of view of Windows, Windows is running on a PC with a hard disk, usually with a capacity of 256GB. When you first install Windows 10, about 21GB of this hard disk will be used for Windows 10 itself. However, from the point of view of the Mac, this “hard disk” is just a file type of “.hdd” that grows and shrinks over time. Initially, the size of this file is 0GB, but as Windows gets installed, it will grow to about 21GB. When this file is created, the default maximum potential size is set to 256GB. As you install applications and create new files, this .hdd file will grow. If this file gets near 256GB, Windows will think that its hard drive is running out of space, and it will give you an “Out of Space” warning. It does not matter if the Mac hard drive has lots of free space since Windows can’t “see” this free space; it can only see what it thinks is a 256GB hard drive that is almost full.

There are three situations that can generate an “Out of Space” warning, and each is handled in a different way.

Situation 1: Windows is out of space, but the Mac has plenty of space.

This happens when the Windows .hdd file is almost full. In priority order, here is how to handle this situation:

Step 1.1: Use the Parallels Toolbox for Windows tools, Clean Drive, and Find Duplicates. (Recall that your Parallels Desktop subscription entitles you to install and use Parallels Toolbox for Mac on your Mac and Parallels Toolbox for Windows in each of your Windows VMs.) These Windows tools will find items in the Windows hard drive that can be deleted, thus freeing up some space. Whether or not this will be sufficient to solve the Out of Space issue depends on how much space these to-be-deleted files consume. (See Figure 1. In the case of this one VM, about 1.8GB of space can be recovered.)

 

Figure 1_Using the Parallels Toolbox for Windows tools Clean Drive and Find Duplicates

Step 1.2: Increase the maximum potential size of the “hard drive” (actually, the .hdd file) used by the Windows 10 VM. You perform this task on your Mac, in the Hardware tab of the Configuration dialog of your virtual machine. (See Figure 2. Click the Properties button to reveal the slider to set the desired new potential size.) This will not initially take any additional space on your Mac, but this will enable the Windows “hard drive” to grow when needed.

Figure 2_Increase the maximum potential size of the Windows hard drive

Situation 2: Windows “thinks” it has plenty of space, but the Mac is out of space.

In this case, the Mac hard drive is almost full. While Windows doesn’t know it, it is also out of space.

Step 2.1: Check to see if there is “empty space” in the Windows .hdd file. If so, reclaim this free space and you may then be done. You do this in the General tab of the Configuration dialog of each of your virtual machines. (See Figure 3. For this particular virtual machine, about 4.1GB of space will be recovered on the Mac.) To reclaim space, Windows must not be running, so shut it down if needed. Then, just click on the Reclaim button shown in Figure 3. This reclamation may only take a minute or two, but I have seen it take more than an hour if there is a lot of space to reclaim, and your .hdd file is very large.

Figure 3_Reclaiming some unused space from the VM

Step 2.2: Use the Parallels Toolbox for Mac tools, Clean Drive, and Find Duplicates. These Mac tools will find items on the Mac hard drive that can be deleted, thus freeing up some space. Whether or not this will be sufficient to solve the Out of Space issue depends on how much space these to-be-deleted files consume. (See Figure 4. In the case of this Mac, about 40GB of space can be recovered.)

Figure 4_Use the Parallels Toolbox for Mac tools, Clean Drive and Find Duplicates

Step 2.3: If you have a fast, high-capacity external SSD, consider moving your VM to this SSD. This blog post will give you the details.

Situation 3: Windows is out of space, and the Mac is out of space.

This case is quite rare but potentially very serious. It is the combination of Situation 1 and Situation 2.

Perform Steps 2.1 and 2.2, and then also perform Steps 1.1 and 1.2. If this doesn’t solve the issue, then perform Step 2.3.

I hope this helps you understand why you may receive an “Out of Space” warning and that it enables you to handle this situation like a pro!