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NinjaOne Backup — Error 306: Snapshot Deleted While Uploading

Audience: T2 Use when: Image backup fails with "Error 306: Snapshot deleted while uploading."

What This Error Means

Lockhart successfully created a VSS snapshot and began uploading data, but the VSS snapshot was deleted (or expired) before the upload completed. Without the snapshot, Lockhart can no longer read the data it was transferring, and the backup fails mid-job.

Why VSS Snapshots Get Deleted Mid-Upload

Cause Explanation
Disk space critically low Windows automatically purges old snapshots when disk space drops below a threshold
Another backup tool cleaning up shadows Old MSP360 agents or Windows Backup tasks removing VSS shadows
Windows Shadow Copy storage limit reached The shadow copy storage area hit its max size — oldest shadows pruned
VSS task scheduler purging shadows Some systems have scheduled tasks that clean shadows aggressively
Upload taking too long Very large first backup + slow internet = snapshot timeout before upload finishes

Step 1 — Check Disk Space on the Source Volume

# Check free space
Get-PSDrive -PSProvider FileSystem | Select Name,
    @{N='FreeGB';E={[math]::Round($_.Free/1GB,1)}},
    @{N='FreePercent';E={[math]::Round($_.Free/($_.Used+$_.Free)*100,1)}}

If any volume is below 15% free — this is the likely cause. Free up space per the Error 307 page, then retry.

Step 2 — Check VSS Shadow Storage Configuration

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

# Check current shadow copies
vssadmin list shadows

# If max size is very small (e.g., 300 MB), increase it:
vssadmin resize shadowstorage /for=C: /on=C: /maxsize=10%

A max size that's too small means Windows purges shadows aggressively as new ones are created.

Step 3 — Check for Conflicting Shadow Cleanup

# Check for scheduled tasks that might be cleaning shadows
Get-ScheduledTask | Where-Object {$_.TaskName -like "*shadow*" -or $_.TaskName -like "*VSS*" -or $_.TaskName -like "*backup*"} |
Select TaskName, TaskPath, State | Format-Table -AutoSize

# Check for old MSP360 / Cloudberry agents still running shadow management
Get-Service | Where-Object {$_.DisplayName -like "*MSP360*" -or $_.DisplayName -like "*Cloudberry*"} |
Select DisplayName, Status

If old backup software is still running shadow management tasks: disable or uninstall.

Step 4 — Address Long Upload Times (Large Initial Backup)

If this is a large first backup and internet upload is slow, the VSS snapshot may be timing out before the upload completes. Options:

  • Bandwidth throttling: Not directly fixing the timeout, but reduces impact on the network and can allow the backup window to be extended without competing traffic
  • Retry strategy: Let NinjaOne's block-aware design resume from the last checkpoint — subsequent attempts will pick up where they left off rather than restarting from scratch
  • Check upload speed: A dental site with <5 Mbps upload and a 500 GB first backup will take days — this is expected

After Resolving

  1. Trigger a manual backup run
  2. Monitor the activity log — confirm the job runs to completion without Error 306
  3. If the initial backup was interrupted, NinjaOne will resume from the last block checkpoint — it does not restart from scratch
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