What Is Volume Shadow Copy (VSS)? How It Works, Benefits, and Troubleshooting

Author: Kostas Tsakiridis, 2BrightSparks Pte. Ltd.

Data loss can cripple individuals and organizations. Backups are necessary to protect precious files from hardware failure, cyberattacks, or accidental deletion.

Data backups are an important part of data management, for a private individual at home to a large computer network at a corporation. Basically, it involves making a copy of any data (i.e. files) deemed important against hardware failures, human mistakes, viruses, calamities and anything else that may corrupt or destroy said data. Having a backup makes data recovery quick and easy thus reducing downtime and headaches.

Consistent, reliable data backups are very important as there is no point having a backup consisting of unusable data. Such backups are almost the same as having no backups at all. On Windows platforms, the Volume Shadow Copy Service (VSS) provides backups that are reliable, consistent, and without downtime.

Let's explore what Volume Shadow Copy is, how it works, its benefits, and how to troubleshoot common VSS issues.

What Is Volume Shadow Copy Service (VSS)?

Microsoft introduced Volume Shadow Copy Service (VSS) in Windows Server 2003. VSS allows backup software to create consistent "snapshots" of files even if the files are being used or updated. Backing up files that were in use before VSS would often cause corruption or require downtime for services.

Today, VSS is integrated into Windows features such as System Restore, Windows Backup, and File History and is a fundamental part of modern data protection methodologies.

How Volume Shadow Copy Works

VSS creates a "point-in-time" snapshot of a file, folder, or entire volume by coordinating three key components:

Requester: The backup software requesting the snapshot (e.g. SyncBackPro).
Writer: The application ensuring data consistency (e.g. SQL Server VSS Writer).
Provider: The system managing snapshot storage.

So the procedure is:

Backup software requests a snapshot.
VSS informs applications to pause writes.
Changes are written to disk.
A snapshot is created.
Normal operations continue as the backup leverages the static snapshot.
This provides you with live and solid backups, even for databases and system files.

Benefits of Using VSS

Using VSS in Windows offers many advantages:

Consistent Backups: Provides consistent copies without taking applications down.
Minimal Downtime: Snapshots are taken almost immediately.
Data Integrity: Avoids file corruption while backing up.
Application Integration: Required for Exchange, Active Directory, and database backups.
Storage Efficiency: Employs "copy-on-write" to reduce space consumption.

According to the National Archives & Records Administration, 60% of businesses that suffer major data loss close their doors within six months, highlighting the critical necessity for robust backup solutions like VSS.

VSS Requirements and Limits

As we mentioned before, VSS has been integrated into certain Windows features. File Versioning is such an example which allows users to access previous versions of files directly from the Windows File Explorer.

Another example is System Restore, which allows users to take a snapshot (aka a restore point) of the operating system at any given moment, something which is very useful before making major changes to it. Windows Update itself will create a restore point before installing any new updates, thus allowing the user to revert to it if something goes wrong during an update.

As with anything else in Windows, there are certain limitations and requirements when it comes to the VSS:

Disk Space Requirement: At least 300 MB of free disk space is needed to create VSS snapshots.
Snapshot Limit: The maximum number of volume snapshots is 64 by default.
Storage Allocation: Windows allocates 10% of the volume space for shadow copies.
Volume Size Restriction: VSS does not support volumes larger than 64 TB.
Writeable Snapshots: Writeable snapshots larger than 64 TB are not supported.
Compatibility Issues: Shadow copies created on older Windows versions may not be usable on newer versions.
VSS is supported on Windows XP and later, and Windows Server 2003 and later.
32-bit VSS applications must run as native 32-bit or 64-bit applications (not under WOW64).

How to Use VSS in Windows

VSS operates behind the scenes and is utilized automatically by robust backup software, such as 2BrightSparks' SyncBackSE and SyncBackPro. They utilize VSS to:

Backup locked and open files.
Take full system backups with no downtime.
Offer options to manually enable or disable the use of VSS.

Moreover, users indirectly experience VSS through features such as:

System Restore Points (generated during Windows updates).
Older Versions of files available through right-clicking within File Explorer.

Troubleshooting Common VSS Issues

VSS errors can interrupt backup operations. Here are some frequent problems and solutions:

VSS_E_BAD_STATE (0x80042301): Incorrect object state.
VSS_E_PROVIDER_VETO (0x80042306): Provider blocked operation.
VSS_E_OBJECT_NOT_FOUND (0x80042308): Missing snapshot object.
VSS_E_WRITER_INFRASTRUCTURE: Problem communicating with VSS writers.
VSS_E_MAXIMUM_NUMBER_OF_SNAPSHOTS_REACHED: Insufficient free disk space.
ConvertStringSidToSid Error: Permission issue.
Volume not added to snapshot: Configuration error.
VSS timeout errors: Operation took too long.
Insufficient disk space: Storage area too small.
VSS writers missing/failed: Causes backup failures.

Troubleshooting Steps

Check Event Logs: Use the Windows Event Viewer to search for VSS errors.
Restart Services: Restart "Volume Shadow Copy" and related services.
Free Up Disk Space: Ensure enough free space on all volumes.
Repair VSS Writers: Restart affected services or reboot the system.
Resolve Conflicting Tasks: Avoid simultaneous maintenance operations.
Run System File Checker: Execute sfc /scannow to fix corrupt system files.
Re-register VSS Components: Use vssadmin list writers and repair as needed.
Temporarily Disable Security Software: Some antivirus tools interfere with VSS.

Final Thoughts: Why VSS Matters

The Volume Shadow Copy Service (VSS) is essential for:

Taking regular backups with no downtime.
Quickly recovering lost or corrupted data.
Supporting application compatibility for the backup.
Sustaining storage efficiency with incremental copies.

For IT experts and Windows users, learning about VSS is the key to building a solid, effective backup and recovery strategy.

If you need a backup solution that supports VSS, look at SyncBackPro and SyncBackSE, both of which have complete support for Volume Shadow Copy operations.

Frequently Asked Questions

Can I manually create a shadow copy?

Yes. You can use the vssadmin command line tool or create restore points manually through System Protection settings in Windows.

What happens if Volume Shadow Copy fails?

If VSS fails, backups may be incomplete or corrupted. It is critical to troubleshoot and resolve VSS errors promptly to ensure reliable data protection.

How do I check if Volume Shadow Copy is enabled in Windows?

You can also use vssadmin list shadows in the Command Prompt to determine if there are already shadow copies present.

Does Volume Shadow Copy slow down my computer?

Normally, no. VSS operates silently and uses minimal resources. However, when there is low disk space or too many snapshots are captured, it could have a minor effect on performance.

Can I delete old shadow copies to free up space?

Yes. You can manually delete old shadow copies using Disk Cleanup or by running vssadmin delete shadows in Command Prompt. Be cautious, as this may remove restore points.