Error: “Mount point already in use” (Drive Letter Conflicts)

The error “Mount point already in use” occurs when Google Drive for Desktop attempts to mount its virtual filesystem to a local drive letter or folder path that is already claimed by another storage volume, network share, or ghost device handle. When this conflict happens, Drive for Desktop cannot initialize its virtual drive, preventing access to streamed Google Drive files in Windows File Explorer or macOS Finder.

Fast Fix

Open Google Drive Settings (gear icon) > Preferences > Advanced Settings. Under Google Drive streaming location, change the assigned drive letter from G: (or your current selection) to an unused letter such as M: or X:. Click Save and restart the application to mount the virtual volume immediately.

Diagnostic Snapshot

Parameter	Specification
Affected Applications	Google Drive for Desktop (Windows & macOS)
Primary Symptom	“Mount point already in use” or “Drive letter G: is unavailable” banner; Drive missing from File Explorer
Common Origin	Mapped network drives (SMB/NFS), USB storage, leftover subst paths, or disconnected VPN share handles
Admin Access Required	No for standard drive letter re-assignment; Yes if resolving system-wide group policy mapped drives or registry locks

Forensic Decision Path

Use the flowchart below to identify the specific mount collision:

[Drive for Desktop Fails to Mount]
  │
  ├─► Is the target drive letter (e.g., G:) visible in File Explorer under Network Locations or Drives?
  │     ├─► Yes (Network Drive) ──► Reassign the conflicting mapped drive or change Drive for Desktop letter.
  │     └─► Yes (Removable / USB) ─► Change persistent USB letter assignment in Disk Management.
  │
  ├─► Is the drive letter invisible in File Explorer but still throwing the error?
  │     ├─► Check Command Prompt (`net use`) ──► Lingering disconnected network session holding the letter.
  │     └─► Check Command Prompt (`subst`) ───► Virtual substituted drive path active in background.
  │
  └─► Is the error occurring on macOS?
        └─► Existing stale mount point located at `~/Library/CloudStorage` or `/Volumes/GoogleDrive`.

What This Means: System Mechanics

Google Drive for Desktop relies on virtual filesystem drivers (such as WinFsp on Windows or File Provider / FUSE extensions on macOS) to expose cloud files as a local block storage device.

During startup, the application requests an exclusive hook on a specific mount target:

• On Windows: It requests a logical drive letter (defaulting to G:\, or the next available letter alphabetically).
• On macOS: It binds to a specific directory path under /Volumes or within the user’s ~/Library/CloudStorage/ directory.

If Windows registers that letter as active, even if the underlying physical or network device is currently offline, the operating system rejects the mount request with a collision error. If the client cannot attach to the designated mount point, file streaming halts completely. If this issue prevents the drive from showing up entirely, see Google Drive Not Showing Up in Windows File Explorer.

Common Causes

• Pre-Existing Network Share Mappings: Corporate login scripts frequently map user network shares to G: or H:, colliding directly with default Google Drive configurations.
• Orphaned SMB Handles: A disconnected network share that was ungracefully unmounted can remain in Windows session tables, reserving the drive letter even if File Explorer displays it as disconnected.
• Virtual Substituted Drives: Scripts or legacy developer tools utilizing the Windows subst command may have mapped an internal folder to the requested drive letter.
• Removable Media & Card Readers: Multi-slot flash card readers or external hard drives can dynamically take over the first available drive letters after a reboot.
• Orphaned macOS Mount Points: An unclean shutdown or crash can leave a ghost folder in /Volumes/GoogleDrive, preventing the operating system from mounting a new volume with the identical directory name. If crashes accompany this behavior, refer to “Google Drive for Desktop encountered an error and has stopped”.

Common Misdiagnoses

• Misdiagnosis: “Google Drive sync is corrupted and the cache needs to be deleted.”
  • Distinction: Clearing the local cache does not release an OS-level drive letter conflict. If the drive letter collision remains, the error persists immediately after rebuilding the cache. To properly manage local cache files when disk bloat is an actual factor, review How to Clear Google Drive Local Cached Files Safely.
• Misdiagnosis: “Account authentication has failed or session has timed out.”
  • Distinction: A mount point conflict is an OS-level filesystem allocation failure, not an OAuth authentication failure. Entering credentials again will not resolve a blocked drive letter. If you are experiencing genuine credential loops, see Resolving “Account disconnected: Please sign in again” Loops.

Resolution Steps

Step 1: Reassign the Drive Letter in Google Drive

The quickest and least disruptive fix is assigning Google Drive a drive letter located further down the alphabet (e.g., S:, V:, or X:):

1. Click the Google Drive icon in the system tray (Windows) or menu bar (macOS).
2. Click the Settings gear > Preferences.
3. Click the Settings gear in the top right of the Preferences window.
4. Scroll down to Google Drive streaming location.
5. Select Drive letter, open the dropdown menu, and pick a letter near the end of the alphabet (e.g., X:).
6. Click Save and select Restart now.

Step 2: Clear Orphaned Network Mappings (Windows)

If you must use a specific drive letter that is blocked by an orphaned connection:

1. Open Command Prompt as Administrator.
2. Run the following command to list active and disconnected network mounts: net use
3. If the conflicting drive letter appears in the list (e.g., G:), remove it by executing: net use G: /delete /y
4. If the drive letter was created via substitution, check and remove it: subst subst G: /d

Step 3: Reassign Colliding Removable Devices

If a permanent secondary hard drive or USB device has taken the letter:

1. Press Win + X and select Disk Management.
2. Locate the volume using the conflicting drive letter in the lower graphical panel.
3. Right-click the volume and select Change Drive Letter and Paths…
4. Click Change, assign a different available letter, and confirm with OK.
5. Restart Google Drive for Desktop.

Step 4: Clear Stale Mount Points (macOS)

If the collision occurs on macOS due to a lingering directory lock:

1. Open Terminal (/Applications/Utilities/Terminal.app).
2. Check for leftover Google Drive directories in /Volumes: Bash ls -la /Volumes
3. If an unmounted directory named GoogleDrive or Google Drive exists, verify it is empty and remove the stale folder: Bash sudo rmdir "/Volumes/GoogleDrive"
4. Restart Google Drive for Desktop.

Admin & Advanced Checks

• Group Policy Script Auditing: If this conflict occurs across multiple managed workstations, review your domain Group Policy Objects (GPOs) under User Configuration > Preferences > Windows Settings > Drive Maps. Ensure automated corporate logon scripts do not claim letters designated for Drive for Desktop deployments.
• Registry-Based Drive Letter Enforcement: Administrators can enforce a universal Drive letter across an entire fleet to prevent collisions by deploying the following registry setting via GPO:
  • Path: HKEY_LOCAL_MACHINE\Software\Google\DriveFS
  • Value Name: DefaultMountPoint
  • Type: REG_SZ
  • Value Data: X: (or desired target drive letter)

Hard Stops

• Hardware Raid / Critical Volume Overlaps: Do not force-unmount or delete drive letter assignments in Disk Management if the volume is marked as System, Boot, or hosts active database files (such as local SQL or Hyper-V virtual disks). Change the Drive for Desktop mount letter instead.