VSS backup timeout on a large file server

Question

We are backing up a large-volume file server using VSS, but the backups keep timing out with the error "VSS_E_HOLD_WRITES_TIMEOUT."

What could be the cause for this?

Answer 1

Dear Gomez Finger,

The error VSS_E_HOLD_WRITES_TIMEOUT occurs when the Volume Shadow Copy Service cannot freeze I/O on the file system long enough to create a snapshot. On large file servers this typically means the VSS writers are waiting for outstanding writes to drain, but the workload is too heavy or the disk subsystem cannot respond within the default timeout. Common causes include extremely high I/O load on the volumes being backed up, insufficient throughput on the storage backend, or filter drivers (such as antivirus or third‑party file system filters) delaying the freeze operation.

To troubleshoot, you should first check the Application Event Log for VSS and VolSnap events around the time of failure, as they will indicate which writer or provider timed out. Running vssadmin list writers immediately after the failure can also show if any writer is in a failed state. If the server is handling continuous heavy writes, consider scheduling backups during lower activity periods or splitting the backup job across multiple volumes. It is also important to ensure the storage firmware and drivers are up to date, and that antivirus or endpoint protection is not scanning the shadow copy creation process. In environments with very large volumes, Microsoft recommends increasing the timeout values via registry (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VSS\Settings) or using hardware VSS providers that can handle high‑volume workloads more efficiently.

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Thank you,

HL.