D: Drive Full — Root Cause & Fix

Date: 2026-06-23 Severity: Critical (D: completely full, Kopia backup failing)

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What Happened

D: drive (1.86 TB) hit 0 bytes free. Kopia backup failed at 8:00 AM trying to write to D:\bak\Kopia_Static.

Root Cause

Two large Windows backup stores had accumulated silently:

Folder	Size	Cause
D:\DESKTOP-TA\	750 GB	Windows File History, accumulating unnoticed
D:\WindowsImageBackup\	228 GB	Old system image backup, never cleaned up

Both folders are invisible to WSL (du) and non-elevated PowerShell — they require an elevated admin session to see. This is why the disk appeared to only have ~876 GB used from WSL, while Windows reported 1.86 TB used.

Why the System Image Accumulated

create_system_image.py has been failing silently for months (March, May, June 2026) with:

[ERROR] Administrator privileges required for system image creation

The cron entry called cmd.exe from WSL, which does not run elevated. So is_admin() returned False and the script exited before running wbAdmin — meaning no retention cleanup ever ran either. The 228 GB was an old manual backup that was never purged.

Why File History Accumulated

Windows File History was enabled and targeting D:, writing to D:\DESKTOP-TA\ (machine name). No retention limit was enforced. It had accumulated 750 GB over an unknown period.

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Diagnosis Steps

1. df -h /mnt/d — confirmed 100% full
2. du -sh /mnt/d/* — showed only ~876 GB (WSL blind spot)
3. Elevated PowerShell script (C:\tmp\disk_check.ps1) — revealed the two hidden folders
4. vssadmin list shadowstorage /for=D: — ruled out VSS shadow copies (only 3.15 GB)

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Fix Applied

1. Deleted D:\DESKTOP-TA\ (750 GB) and D:\WindowsImageBackup\ (228 GB) from elevated PowerShell
2. Disabled Windows File History service (fhsvc set to Disabled)
3. Removed broken cron entry for create_system_image from WSL crontab
4. Created run_system_image.bat wrapper in my_backup/ for Task Scheduler use
5. Created C:\tmp\setup_system_image_task.ps1 to register a proper Task Scheduler task

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Remaining Action (Manual)

Run from elevated PowerShell to complete the fix:

& C:\tmp\setup_system_image_task.ps1

This creates the Task Scheduler task \FSS\FSS System Image Backup (Monthly) that:

• Triggers on the 1st of every month at 4:00 AM
• Runs as the current user with RunLevel Highest (proper admin elevation)
• Logs to my_backup/logs/system_image.log
• Fires heartbeat to job monitor on completion

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Prevention

• System Image: Task Scheduler (not WSL cron) is required for any job needing admin elevation. WSL cron → cmd.exe does NOT elevate.
• File History: Disabled. Kopia covers all file backup needs — File History is redundant and dangerous on a data drive without retention limits.
• Monitoring gap: Neither DESKTOP-TA nor WindowsImageBackup were visible from WSL or job monitor. Add a monthly disk-usage check from elevated context if this is a concern going forward.
• D: disk headroom: After fix, ~980 GB free. System image backups (3 max × ~75 GB ≈ 225 GB) will grow back into D:\bak\System_Images\ — retention is managed by the Python script.