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NinjaOne Backup — Error 308: Unable to Determine Free Space

Audience: T2 Use when: Backup fails with "Error 308: Unable to determine free space."

What This Error Means

Lockhart is trying to determine available disk space before starting the backup (a standard pre-flight check), but the WMI (Windows Management Instrumentation) query it uses to get that information is failing or returning unexpected data. This is a Windows infrastructure issue, not a disk space issue.

Most Likely Cause: WMI Corruption

WMI is the Windows subsystem that provides system information to management tools — including NinjaOne and Lockhart. If the WMI repository is corrupt or a WMI query is timing out, Error 308 appears.

Step 1 — Test WMI Is Functioning

# Basic WMI query for disk info — this is similar to what Lockhart runs
Get-WmiObject Win32_LogicalDisk | Select DeviceID, FreeSpace, Size

# If this hangs or returns errors: WMI is the problem
# If it returns values: WMI is healthy — look elsewhere (Step 3)

Step 2 — Repair WMI Repository

# Stop WMI service
Stop-Service Winmgmt -Force

# Repair the WMI repository
winmgmt /resetrepository

# Restart WMI
Start-Service Winmgmt

# Verify
Get-Service Winmgmt | Select Status
Get-WmiObject Win32_LogicalDisk | Select DeviceID, FreeSpace, Size

If winmgmt /resetrepository fails: try /salvagerepository instead:

winmgmt /salvagerepository

After repair: reboot the machine, then trigger a manual backup run.

Step 3 — Check for Disk Volume Issues

If WMI is healthy but Error 308 persists, the volume itself may have an issue that prevents space queries:

# Check disk status
Get-Disk | Select Number, FriendlyName, OperationalStatus, HealthStatus

# Check for RAW or uninitialized volumes
Get-Volume | Select DriveLetter, FileSystemType, HealthStatus, OperationalStatus |
Where-Object {$_.FileSystemType -eq "Unknown" -or $_.HealthStatus -ne "Healthy"}

A RAW volume (filesystem unreadable) will cause 308 on any management tool query.

Step 4 — Verify the Volume Is Mounted and Accessible

# List all drives and confirm expected drive letters exist
Get-PSDrive -PSProvider FileSystem | Select Name, Root, @{N='FreeGB';E={[math]::Round($_.Free/1GB,1)}}

# If a drive letter is missing that should be present: investigate disk management

After Repair

  1. Confirm WMI queries return data without hanging
  2. Trigger a manual backup run from NinjaOne
  3. Monitor for completion — Error 308 should not recur if WMI was repaired

Escalate to T3 If:

  • winmgmt /resetrepository and /salvagerepository both fail
  • WMI appears healthy but Error 308 persists
  • A volume is showing as RAW — filesystem corruption requiring urgent data recovery assessment
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