Troubleshooting VSS

What is VSS?

Volume Shadow Copy Service (VSS) is a Microsoft technology for taking consistent, point-in-time snapshots of a disk volume. A VSS Writer is an extra software plugin that detects when a snapshot is being taken and makes sure application-specific files are in a safe state on disk. Magnus Box uses VSS when a Protected Item has Take filesystem snapshot turned on, and for backup types that invoke a single VSS Writer (or one of its components) to back up only the files it protects.

Important notes

VSS snapshots don't work over network paths. Instead of snapshotting over the network, install the backup app on the device that holds the original data.
VSS problems can happen when another backup product is also installed and is interfering with VSS. Many backup products have their own snapshot provider, which can conflict with others. Stop or remove the other product to see if the problem goes away.
VSS errors often include a code in the form 0xXXXXXXXX. This code comes from Windows, not Magnus Box, and usually says why the snapshot or writer failed. Search for the code to find Microsoft's guidance.

Jump to an error

"VSS Error: Couldn't take snapshot. The shadow copy provider had an unexpected error..."
"0x80042316: Another shadow copy creation is already in progress"
"A device which does not exist was specified" or "The device is not ready"
"An imminent failure indicates either bad privileges or WOW64"
"Couldn't initialize VSS (0x80070005: Access denied)"

Common fixes

Make sure VSS is running

Open Services (services.msc).
Find Volume Shadow Copy and double-click it.
Check the startup type. The default is Manual, which is fine because Windows starts the service when a snapshot is requested. If it's set to Disabled, set it back to Manual (or Automatic).
Check the service status. If it's stopped, click Start.

Check the VSS writers

Open an elevated command prompt and run vssadmin list writers. This lists the current writers and shows any that failed, with their own error codes. It helps you find which writer caused the failure.

Fixing transient issues

Some VSS errors happen when the machine is having difficulty holding I/O writes while the snapshot is taken. Wait about 10 minutes and try again, or restart the machine. If it keeps happening, it may point to a failing hard drive.

On a Hyper-V host with several guests, leftover components from an old backup product (for example StorageCraft) inside the guests can cause VSS failures. Uninstalling them from the guests should fix it.

Error "VSS Error: Couldn't take snapshot. The shadow copy provider had an unexpected error..."

Full message: "VSS Error: Couldn't take snapshot. The shadow copy provider had an unexpected error while trying to process the specified operation".

Possible causes and fixes:

Backing up a mapped network drive. You can't use VSS on a network share. Turn off Take filesystem snapshot for that Protected Item, or install the backup app on the machine that holds the data.
Shadow storage isn't configured or is too small on the source drive. Check and change it from an elevated command prompt:
- To check the current limit: vssadmin list shadowstorage
- To change the limit: vssadmin Resize ShadowStorage /For=X: /On=X: /Maxsize=XX%
A snapshot was already being created when the backup started. See Another shadow copy creation is already in progress. Restarting the Volume Shadow Copy service can clear a stuck snapshot. From an elevated command prompt, run net stop vss and then net start vss. If that doesn't help, restart the server.
Another backup product is installed with its own snapshot provider, which conflicts with VSS.
An Advanced Format drive is connected. VSS snapshots have been known to fail because of this.
A VSS writer is missing or failed. Run vssadmin list writers from an elevated command prompt and check that all writers are listed with no errors.

Error "Another shadow copy creation is already in progress"

Full message: "VSS Error: Couldn't take snapshot (IVssBackupComponents::StartSnapshotSet: 0x80042316: Another shadow copy creation is already in progress".

Cause: VSS can hold several snapshots at once, but it can only create one at a time. Another snapshot (from Windows, another backup product or another Magnus Box job) was being created when this backup started.
Fix: retry the backup later, or move its schedule 30 minutes earlier or later so it doesn't overlap with the other snapshot.

Error "A device which does not exist was specified" or "The device is not ready"

The messages look similar to these:

Open failed because: open \\?\GLOBALROOT\Device\HarddiskVolumeShadowCopy16\FOLDER\FOLDER\FILE: A device which does not exist was specified
Error for \\?\GLOBALROOT\Device\FOLDER\FOLDER\FILE: BackupRead \\?\GLOBALROOT\Device\FOLDER\FOLDER\FILE: The device is not ready

This is a VSS snapshot error. It means the snapshot was probably destroyed while the backup was still reading from it. Malware or "cleanup" programs can delete snapshots. Windows also deletes snapshots when the disk is low on space and the shadow storage area runs out of room.

Run the backup again. The problem may have been temporary.
Check the free disk space on the device, and check the shadow storage size (see above).
Check for software on the device that deletes shadow copies.

Error "An imminent failure indicates either bad privileges or WOW64"

This message appears in the client log. It comes from Windows, not Magnus Box.

Cause: the backup app's background service doesn't have permission to take a VSS snapshot. The installer grants this permission, so something on the machine has removed it since.
In services.msc, check that the Magnus Box service runs as the NT SERVICE\backup.delegate account. A Group Policy may have changed it.
If the device is joined to an Active Directory domain, a domain policy may be overriding the permissions the installer set.
Workaround: reinstall the backup app to restore the correct permissions. Then watch the logs for the same error. The time it comes back tells you when the permissions changed, which helps you find the policy or tool responsible.

Error "Couldn't initialize VSS (0x80070005: Access denied)"

This error comes from Windows, but it shows up in the Magnus Box logs.

Affects: Windows Server, many versions.
Known cause: adding the DHCP role to the server.
Fix: give the Network Service account Full Control of the registry key HKLM\System\CurrentControlSet\Services\VSS\Diag. See Microsoft's article VSS error 8193 when you restart the Cryptographic Services service and this Spiceworks discussion.

Still stuck?

Email support@magnusbox.com with the user name, the device name, the job log and the output of vssadmin list writers and vssadmin list shadowstorage.

For VSS errors when using DESlock+ encrypted drives, see Error "Couldn't take snapshot: The specified object was not found" using DESlock+.