Troubleshooting VSS for Q-Hybrid

Alike Q-Hybrid, and physical backups rely on the proper functioning of Microsoft's VSS snapshots on the target system. By default, Q-Hybrid backups will attempt to create a VSS snapshot that includes all volumes that have a drive letter assigned. Please note, VSS snapshots are only available for NTFS filesystems.

If you encounter a snapshot/vss error, you can start troubleshooting on the target system, by attempting to take a snapshot manually:

Windows Server:

vssadmin create shadow /for=c:

Windows 10:

Run with administrative rights:

powershell.exe -Command (gwmi -list win32_shadowcopy).Create('c:\','ClientAccessible')

Often times, the Shadow Store, where the VSS snapshots resize has insufficient room to take a new snapshot. While Microsoft recommends 20% of a volume be allocated to the Shadow Store, sometimes that isn't enough. To increase it, you can run the following command (with your desired values), from an administrative command prompt:

vssadmin Resize ShadowStorage /For=C: /On=C: /MaxSize=30%

Note: the "MaxSize" can also be a specific amount, such as 500GB instead of a percent value.

Another common problem is when one or more VSSWriter has a failure. To list all the registered VSSWriters, and their status, you can run the following command:

vssadmin list writers

Ideally, you should see a list of writers, in a "Stable" state, like the following:

Writer name: 'Microsoft Hyper-V VSS Writer'

  Writer Id: {66841cd4-6ded-4f4b-8f17-fd23f8ddc3de}

  Writer Instance Id: {a6c359f8-4028-455c-80e3-667ec74d7e51}

  State: [1] Stable

  Last error: No error

However, if you see a state of Failed, or an error of "Retryable error", you can always try restarting the corresponding Windows Service for that Writer.

A list of common VSS Writers, and their related Windows Services are as follows:

VSS Writier Name Windows Service to restart

ASR Writer Volume Shadow Copy

BITS Writer Background Intelligent Transfer Service

Certificate Authority Active Directory Certificate Services

COM+ REGDB Writer Volume Shadow Copy

DFS Replication service writer DFS Replication

DHCP Jet Writer DHCP Server

FRS Writer File Replication

FSRM writer File Server Resource Manager

IIS Config Writer Application Host Helper Service

IIS Metabase Writer IIS Admin Service

Microsoft Exchange Replica Writer Microsoft Exchange Replication Service

Microsoft Exchange Writer Microsoft Exchange Information Store

Microsoft Hyper-V VSS Writer Hyper-V Virtual Machine Management

MSMQ Writer (MSMQ) Message Queuing

MSSearch Service Writer Windows Search

NPS VSS Writer COM+ Event System

NTDS Active Directory Domain Services

OSearch VSS Writer Office SharePoint Server Search

OSearch14 VSS Writer SharePoint Server Search 14

Registry Writer Volume Shadow Copy

Shadow Copy Optimization Writer Volume Shadow Copy


SPSearch VSS Writer Windows SharePoint Services Search

SPSearch4 VSS Writer SharePoint Foundation Search V4

SqlServerWriter SQL Server VSS Writer

System Writer Cryptographic Services

TermServLicensing Remote Desktop Licensing

WDS VSS Writer Windows Deployment Services Server

WIDWriter Windows Internal Database VSS Writer

WINS Jet Writer Windows Internet Name Service (WINS)

WMI Writer Windows Management Instrumentation

Additional MS VSS Resources

All of the following tools can be found in the Microsoft Windows Software Development Kit (SDK). (Latest version of the SDK). These tools can be helpful in troubleshooting

Vshadow - VShadow is a command-line tool for taking and managing VSS snapshots. Note that the create function is not available in desktop versions of Windows

VSS Diagnostics - Vsdiagview and Vssagent are tools that can be used to troubleshoot VSS applications. 

BETest - BETest is a VSS requester that tests advanced backup and restore operations.

Vswriter The Test Writer is a utility that you can use to test VSS requester applications. This writer can be configured to perform almost all of the actions that a VSS writer can perform. The Test Writer also performs checks to ensure that the requester has dealt with these writer actions properly.

VssTrace - To collect tracing information for the VSS infrastructure, you can use the VssTrace tool, the Logman tool, or the Tracelog tool. Logman is a trace controller for trace events and performance counters. Tracelog is included in the Windows Driver Kit (WDK).