Storage space shows pool capacity almost full but file explorer shows much more free

T C 20 Reputation points

I have three ssd same make/model with 465 GB pooled in a two-way mirror (P: drive) showing 1.36 TB is being used. File Explorer shows 495 GB is being used with 900 GB free. If I search P: thru Explorer I can confirm that I am using 495 GB. I have some VMs through Hyper-V that I have successfully run for over a year. I don't think there is an issue with the VMs.

This is what I suspect: I recently downloaded all my Google Photos via its "Take-Out" function. I split my data into 50 GB zip files, and there were a total of 8 zip files. Since my storage space had 900 GB free I assumed downloading 400 GB of pictures/videos wouldn't be an issue. All files were downloaded, but when I started to unzip them I received out of space notices by file explorer. I couldn't unzip any of the files.

I got busy with work and now today one of my VMs failed due to being out of storage capacity. So I moved all the zip files off into various ssd and thumb drives, but the storage space still shows low capacity. The vm booted back up without any issues so far, but I need to resolve this before something bad happens.

All three drives show good health but with 84% used.

#I am not professional trained, but my understanding of a two-way mirror is that half of the pooled data is used up for a back up, if that's true, then instead of 1.36 TB of starting space I would only have 680 GB. But if that's is also true, then if I am using (per file explorer) 495 GB of space from 680 GB would be 73% used, not 84%. Or I could be misunderstanding twso-way mirror.

Can anyone help?

Windows 11
Windows 11
A Microsoft operating system designed for productivity, creativity, and ease of use.
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  1. Ian Xue (Shanghai Wicresoft Co., Ltd.) 34,196 Reputation points Microsoft Vendor

    Hi T C,

    Hope you're doing well.

    First, regarding your understanding of two-way mirrored storage spaces: You're correct that a two-way mirror provides redundancy by storing data on two drives. However, the actual implementation is more nuanced. Storage Spaces do not mirror entire drives; instead, they allocate and mirror individual data slabs. These slabs are distributed proportionally across the available disks based on their sizes¹. So, it's not a simple 50% backup scenario.

    Now, let's address the discrepancy between the reported space usage and the actual data you've stored:

    1. You mentioned that your pooled SSDs show 1.36 TB used. This includes both the data and the mirrored redundancy. However, the actual usable space (after mirroring) is less than the sum of the individual drive capacities. In your case, with three 465 GB SSDs, the usable space would be approximately 465 GB (since it's a two-way mirror). So, your starting usable space is indeed around 680 GB, not 1.36 TB.
    2. File Explorer shows 495 GB used, which aligns with your actual data. However, it's essential to understand that the reported space usage includes both the data and the mirrored redundancy. Therefore, the 84% usage you're seeing likely accounts for both the data and the mirrored copies.
    3. When you downloaded your Google Photos, you created 50 GB zip files. These files are part of the data stored in your storage space. However, unzipping them requires additional temporary space. If your available space was insufficient during the unzipping process, it could have caused the out-of-space notices.
    4. Storage Spaces use thin provisioning, meaning that the logical volume can appear larger than the actual physical space allocated. As long as you don't exceed the physical capacity, the volume can continue to grow. When you moved the zip files to other drives, the logical volume size didn't change immediately because the space is allocated on demand.

    To address the issue:

    (1) Confirm that your VMs are functioning correctly after the storage space adjustments.

    (2) Consider freeing up additional space by removing unnecessary files or optimizing your storage usage.

    Best Regards,

    Ian Xue

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    It seems that the user is experiencing an issue where the storage space pool is showing almost full, but File Explorer is showing much more free space. This could be due to the user recently downloading a large amount of data and attempting to unzip it, which caused out of space notices. The user moved the files off the pooled drives, but the storage space still shows low capacity.

    Regarding the user's understanding of a two-way mirror, it is correct that half of the pooled data is used for backup. However, the calculation of 73% used is incorrect. If the user has 680 GB of usable space, and is currently using 495 GB, then the percentage used would be 72.8%, which is close to the reported 84%.

    To resolve this issue, the user can try running Disk Cleanup to free up space, or move more files off the pooled drives. It may also be helpful to check if there are any large files or folders taking up space that can be deleted.

    Answer: The user may be experiencing an issue with storage space due to recently downloading a large amount of data and attempting to unzip it, which caused out of space notices. Moving the files off the pooled drives did not resolve the issue. The user can try running Disk Cleanup or deleting large files or folders to free up space.