Hyper-V backup job fails to create shadow copy with default shadow storage limit

Challenge

Backup or replication of a Hyper-V VM fails. In the Windows event logs on the Hyper-V host server, there is an error with ID 8193 from source VSS:

Volume Shadow Copy Service error: Unexpected error calling routine Cannot find anymore diff area candidates for volume \\?\Volume{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxx}\ [0]. 

Note: This KB specifically addresses the error “cannot find anymore diff area candidates for volume.” There are a variety of possible VSS errors with ID 8193.

Veeam Backup & Replication reports a general error about snapshot creation failure:

Unable to create snapshot (Microsoft Software Shadow Copy provider 1.0) (mode: Crash consistent). Details: Unknown status of async operation
The shadow copy provider had an unexpected error while trying to process the specified operation.
--tr:Failed to create VSS snapshot.
--tr:Failed to perform pre-backup tasks.

Cause

The Volume Shadow Copy Service is unable to allocate disk space to create a shadow copy because the maximum size of the shadow storage area is too small.

Solution

Increase the shadow copy storage area for the volume listed in the error event, or set the maximum size to “No limit.”

To identify the volume listed in the event, run “mountvol” from a command prompt; below the usage information will be a list of volume GUIDs and their associated mount points, if any.

This size of the shadow storage area can be changed in the Shadow Copies utility, or from the command line.

Note: By default, each volume stores its own shadow copy. For example, a shadow copy of a CSV mapped to C:\ClusterStorage\Volume8 would also be stored on C:\ClusterStorage\Volume8. Do not change the location of the shadow copy storage area on a Hyper-V host server.

Shadow Copies Utility

To access the utility, right click any volume and choose Configure Shadow Copies.

In the Shadow Copies utility:

1. Select the volume with insufficient space;
2. Click Settings…
3. In the “Maximum size” box, either increase the limit, or choose “No limit”.

A limit at least 20% of the total volume size may be needed on busy servers.

Command Line

All commands below should be run from an administrator command prompt.

Use vssadmin list shadowstorage to view existing shadow storage associations. If no association exists for any volume, the command response will be “No items found that satisfy the query.”

If no association is listed for the volume, run vssadmin add shadowstorage to set the size of the shadow storage area. For example, on a 1 TB volume labeled D:

vssadmin add shadowstorage /for=D: /on=D: /maxsize=200GB

If a shadow storage association already exists, run vssadmin resize shadowstorage to set the size of the shadow storage area. For example, on a 1 TB volume labeled D:

vssadmin resize shadowstorage /for=D: /on=D: /maxsize=200GB

The /maxsize parameter is not optional, but can be set as /maxsize=UNBOUNDED

 

More Information

It is not necessary to enable shadow copies for shared folders. “Next Run Time” should show “Disabled.”