Troubleshooting Storage Space Error When Copying Files in File Explorer with WSL on Ubuntu Server 24.04

Users encountering a storage space error when copying files from an 8TB EXT4 NAS drive via WSL on Ubuntu Server 24.04 are likely facing a mismatch between Windows File Explorer's volume management and WSL2's Linux kernel view of the filesystem. This issue typically arises because Windows does not natively mount EXT4 volumes in a way that allows seamless integration with the WSL2 virtual hard disk (vhdx) or standard Linux block devices, leading to perceived capacity discrepancies or permission errors during copy operations.

Understanding the Storage Discrepancy

The core of this problem lies in how Windows handles external drives formatted with Linux-native filesystems like EXT4 compared to how WSL2 interacts with them. When you connect an 8TB NAS drive formatted as EXT4, Windows File Explorer may not recognize it properly, or it may show incorrect free space information because it lacks native drivers for EXT4. In contrast, WSL2 runs a full Linux kernel inside a lightweight utility VM. If the drive is accessible within the WSL2 environment but shows "no space left" or similar errors in File Explorer, it indicates that the two environments are viewing the storage differently. Windows relies on NTFS or exFAT for reliable cross-platform compatibility. EXT4 is not supported natively by the Windows kernel for general file system operations. Therefore, when you attempt to copy files using File Explorer, you might be trying to access a path that Windows cannot interpret correctly, or the drive is mounted in a way that restricts write access. The error often manifests as a generic "storage space" warning, which can be misleading since the physical drive has ample space. Instead, the issue is usually related to how the filesystem is exposed to the Windows host versus the WSL2 guest.

Distinguishing Between Host and Guest Views

It is crucial to determine whether the error occurs within the WSL2 terminal or in the Windows File Explorer interface. If the error appears in WSL2 when running commands like cp or rsync, the problem is likely related to the WSL2 vhdx size limit or the specific mount configuration of the EXT4 drive. WSL2 stores its state in a dynamic VHDX file located at %LOCALAPPDATA%\WSL\wsl.vhdx. By default, this file grows up to 256GB. If your WSL2 distribution or mounted drives exceed this, you may encounter space errors. However, for an external 8TB drive, the issue is rarely the vhdx size unless you are storing data *inside* the WSL2 rootfs rather than on the mounted external drive. If the error occurs in File Explorer, it is almost certainly because Windows cannot read the EXT4 partition directly. You cannot simply drag and drop files from an EXT4-formatted NAS drive into Windows without third-party software or a proper bridging mechanism. WSL2 provides access to Windows drives via /mnt/c, but the reverse—accessing a Linux-formatted drive from Windows—is not supported out-of-the-box.

Verifying Drive Access in WSL2

To troubleshoot effectively, first verify that the EXT4 drive is correctly recognized and mounted within the WSL2 environment. Open your Ubuntu Server 24.04 terminal and check if the drive appears in the output of lsblk or df -h. If the drive is listed, note its device name, such as sdb1. Next, try creating a mount point manually:

sudo mkdir -p /mnt/nas
sudo mount /dev/sdb1 /mnt/nas

If this command fails, the drive might already be mounted elsewhere, or there could be permission issues. Check the current mounts with mount | grep sdb. Once mounted, test writing a small file to ensure the filesystem is functional within Linux:

touch /mnt/nas/test_file.txt
ls -l /mnt/nas/test_file.txt

If these steps succeed, the EXT4 drive is healthy and accessible within WSL2. The next step is to understand how to move data between this Linux-mounted location and Windows.

Bridging WSL2 and Windows File Explorer

Since Windows cannot natively browse EXT4 partitions, you must use the WSL2 interoperability features to transfer files. The recommended approach is to copy files from the mounted EXT4 drive into a Windows-accessible directory, such as /mnt/c/Users/YourName/Documents. From there, you can access them normally in File Explorer. Use the wslpath utility to convert paths if needed, but direct copying is usually straightforward:

cp /mnt/nas/large_file.iso /mnt/c/Users/YourName/Downloads/

Be aware that network shares (SMB/CIFS) connected from Windows are also visible in WSL2 under /mnt/. If your NAS is accessed via SMB in Windows, it will appear in WSL2. However, performance over SMB can be slow, and some file attributes may not translate perfectly. For high-volume transfers, keeping the data in its native EXT4 format within WSL2 and using rsync or tar to export to Windows is more efficient. For users experiencing broader WSL2 configuration issues, such as update failures or lock errors, refer to our guide on Error Updating Ubuntu on WSL to ensure your subsystem is stable before performing large data operations.

Addressing Persistent Errors

If you continue to see storage errors despite correct mounting, consider the following checks:

• VHDX Size Limit: Ensure your WSL2 vhdx is not full. Use wsl --shutdown then check the size of wsl.vhdx. If necessary, resize it using vhdutil or PowerShell's Resize-VHD cmdlet.
• Permission Issues: Verify that your user has write permissions to the mount point. Use chmod or chown if necessary.
• File System Corruption: Run fsck on the EXT4 drive within WSL2 to check for errors: sudo fsck /dev/sdb1.

In rare cases, conflicts with other WSL instances or hyper-v configurations can cause unexpected behavior. If you suspect a deeper system conflict, checking for related locking issues might help. See Fixing WSL 'Failed to take /etc/passwd lock: Invalid argument' Error for troubleshooting similar subsystem anomalies.

Frequently Asked Questions

Why does Windows show the EXT4 drive as having no space?

Windows lacks native drivers for EXT4, so it often misinterprets the filesystem structure, showing zero free space or marking the drive as unreadable. This is a display limitation of the Windows host, not an actual lack of storage on the NAS.

Can I read EXT4 drives directly in Windows File Explorer?

No, not without third-party software. Windows does not support EXT4 natively. You must either use Linux-compatible file managers within WSL2 or convert the data to a Windows-readable format like NTFS or exFAT before accessing it via File Explorer.

How do I increase the WSL2 VHDX size limit?

You can increase the dynamic VHDX size by shutting down WSL with wsl --shutdown and then using PowerShell to resize the wsl.vhdx file. This prevents "no space" errors if your Linux distributions or internal data exceed the default 256GB limit.

Is it faster to use SMB or EXT4 for transfers?

Keeping data in native EXT4 within WSL2 and using Linux tools like rsync is generally faster and more reliable for large datasets. SMB introduces overhead and potential metadata translation issues, which can slow down bulk copy operations significantly.

What should I do if the drive mounts but I get permission denied?

Check the ownership of the mount point using ls -ld /mnt/nas. If the files are owned by root, you may need to adjust permissions using chmod or remount the drive with specific UID/GID options in your /etc/fstab or mount command.