Skip to main content

NinjaOne Backup — Error 307: Low Disk Space Preventing VSS Snapshot

Audience: T1 / T2 Use when: Backup fails with "Error 307: Volume has less than 20% disk space available — may be insufficient to complete a VSS snapshot."

This is a warning that can escalate into a hard VSS failure (Error 132) if not addressed. The source volume doesn't have enough free space for VSS to create its scratch space for the snapshot.

Why VSS Needs Free Space

VSS creates a temporary "difference area" on the same volume it's snapshotting. If the volume has less than roughly 10–20% free space, VSS may fail to allocate this area and the snapshot fails before the backup can start. Error 307 is NinjaOne's heads-up that you're approaching that threshold.

Step 1 — Check Current Disk Space

# Check all volumes on the protected device
Get-PSDrive -PSProvider FileSystem | Select Name,
    @{N='UsedGB';E={[math]::Round($_.Used/1GB,1)}},
    @{N='FreeGB';E={[math]::Round($_.Free/1GB,1)}},
    @{N='TotalGB';E={[math]::Round(($_.Used+$_.Free)/1GB,1)}},
    @{N='FreePercent';E={[math]::Round($_.Free/($_.Used+$_.Free)*100,1)}}

Flag any volume below 20% free that is included in the backup plan.

Step 2 — Identify What's Using the Space

# Find the largest folders on the C: drive (adjust drive letter as needed)
Get-ChildItem C:\ -Recurse -ErrorAction SilentlyContinue |
Where-Object {!$_.PSIsContainer} |
Group-Object DirectoryName |
Select Name, @{N='SizeGB';E={[math]::Round(($_.Group | Measure-Object Length -Sum).Sum/1GB,2)}} |
Sort-Object SizeGB -Descending |
Select-Object -First 20 | Format-Table -AutoSize

Common culprits at dental sites:

Cause Location Fix
Windows Update cache C:\Windows\SoftwareDistribution\Download Run Disk Cleanup as Admin → clean up Windows Update files
Windows Installer patch cache C:\Windows\Installer Do NOT delete — can break uninstalls
Old IIS/application logs C:\inetpub\logs or application-specific Compress or archive logs older than 90 days
Dental app temp files Varies by app Check app-specific temp paths
Previous VSS shadow copies Hidden vssadmin list shadows — delete old ones if excessive
Pagefile / hibernation C:\pagefile.sys, C:\hiberfil.sys Evaluate — reducing pagefile is a T2/T3 conversation

Step 3 — Run Disk Cleanup

# Launch Disk Cleanup in extended mode (includes system files)
# Run as Administrator
cleanmgr /sageset:65535
cleanmgr /sagerun:65535

Or interactively: search "Disk Cleanup" → select the drive → Clean up system files → check Windows Update Cleanup, Temporary files, Delivery Optimization Files.

Step 4 — Clear Excessive VSS Shadow Copies

If old shadow copies are consuming space on the volume:

# List existing shadow copies
vssadmin list shadows

# Delete all shadow copies on C: (safe — NinjaOne creates new ones)
vssadmin delete shadows /for=C: /all /quiet

Step 5 — Verify VSS Shadow Storage Allocation

# Check how much space VSS is allocated for shadow storage
vssadmin list shadowstorage

# If the Max Size is set to a small fixed value, increase it:
# vssadmin resize shadowstorage /for=C: /on=C: /maxsize=10%

After Freeing Space

Once free space is above 20% on the affected volume:

  • Trigger a manual backup run from NinjaOne
  • Confirm the backup completes without Error 307
  • Monitor for the next two nights to ensure retention trimming doesn't bring space back below threshold

When Error 307 Becomes Urgent

If the volume is approaching 10% or less free: this is an immediate risk. Dental databases (SQL Server, MySQL, Actian) can also fail or corrupt when the hosting volume runs out of space. Flag to the AM for a capacity conversation if the root cause is data growth rather than temp files.

Back to top