Skip to main content
CrashPlan Support

Understanding And Troubleshooting Backing Up Open Files With Windows VSS

Applies to:
  • CrashPlan for Home
Need enterprise or small business documentation?
This article is intended for CrashPlan for Home users. For Code42 CrashPlan and CrashPlan for Small Business documentation, read this page on our enterprise support site.


CrashPlan supports backing up open files in Windows by using the Volume Shadow Service (VSS) that is built into the operating system. This is the same service that Windows' built-in backup application, NT Backup, uses. This article describes:

  • The technical details about how CrashPlan and VSS work together
  • The limitations of this approach
  • Recommended solutions for errors associated with VSS

Under the hood

At a high-level, here's how the CrashPlan app coordinates with VSS to back up open files:

  1. CrashPlan starts to back up.
  2. CrashPlan fails to back up an open file.
  3. CrashPlan requests a snapshot from VSS for all local drives.
  4. VSS sends a freeze to all registered “writers,” such as, Exchange, Outlook, and SQL Server.
  5. Writers flush their state to disk.
    Note: If an application isn't a known writer then it may or may not work. The application isn't given a chance to flush its state to disk. The snapshot will be exactly as it exists on disk.
  6. VSS creates snapshot.
  7. VSS provides CrashPlan with details to access the new snapshot.
  8. CrashPlan backs up ALL files using the snapshot until it reaches a file that has changed since the snapshot was created or the backup session finishes.

For more details see the TechNet article from Microsoft MSDN.


Using VSS allows CrashPlan to back up open files. However, VSS has some restrictions and limitations. For instance, the program that is writing to the open file needs to support VSS, not just CrashPlan. In addition, the following conditions must exist for VSS to be successful:

  • VSS must be enabled
  • There must be devices enabled and associated to the VSS
  • The Windows user account must have full access to VSS
  • Only local disks are supported
  • An NTFS partition must exist on an internal drive, with at least 100 MB free space for the shadow copies
  • Free space must be available on drives containing locked files
  • In Windows XP, only one shadow volume can be created per drive at any one time

In addition, VSS is known to fail if there is too much disk activity.

You may see the message “Unable to backup n files” in the history log if CrashPlan is unable to back up an open file via VSS. If this occurs, CrashPlan will try again later and may succeed if the file has been closed.

Applications known to fail

These applications don't appear to work well with VSS:

While the file(s) may back up, they might not restore to a state that the application can use. We suggest closing these applications before backing up. Alternatively, you can use a known method for creating a backup of the application files, then use CrashPlan to back up the backup. You can also disable the Back up open files option so that CrashPlan makes hourly attempts until it no longer detects that the file is open and then backs it up.

Limitations when installed per user

When you install per user, CrashPlan has the same level of access as the user account, so it does not have full access to VSS. Files that are left open may not back up regularly. If files are not backing up you will see the message “Unable to backup n files” in the history log. If this occurs, CrashPlan will try again later; if the file is closed, then backup will succeed.

Supported versions of Windows

All versions of Windows that meet the CrashPlan system requirements support VSS.

32 and 64-bit compatibility

If you are running a 32-bit version of Windows, then it is important that you are using the 32-bit version of the CrashPlan app. Likewise, if you are running a 64-bit version of Windows, then it is important that you are using the 64-bit version of the CrashPlan app. You may experience VSS issues if the version of your operating system and the CrashPlan app are not compatible. See our instructions for installing the CrashPlan app for links to the appropriate version of the CrashPlan app for your operating system.

Windows Server 20031

Service pack 1 is highly recommended for Windows Server 2003. See the following hot fixes from Microsoft:

  • Microsoft Support Hot Fix: Time-out errors occur in Volume Shadow Copy service writers, and shadow copies are lost during backup and during times when there are high levels of input/output
  • Microsoft Support Hot Fix: Volume Shadow Copy Service (VS Volume Shadow Copy Service (VSS) update package is available for Windows Server 2003)

1 Windows Server 2003 is no longer a supported operating system. For details, see Platform Retirement And End of Support For Windows Server 2003.

Recommended solutions

Unable to back up files

If your backup never reaches 100%, or you see the message "unable to back up n files" in your history log, consult our Unable To Back Up Files troubleshooting article.

Failing to back up open files and 0x8004230f error displays in logs

If you see the following in your logs:

Volume C:\ not supported. COM object method returns error code: **0x8004230F**

This is an unexpected provider error. It comes from Microsoft VSS. The Microsoft default provider is very reliable, so we suspect a 3rd party VSS provider may be causing the issue.

This may be caused by the following:

  • TrueCrypt encrypted drives
  • Disk partitioning utilities like Acronis (cloning process may cause VSS system to fail)
  • Defragmentation running at the same time

First make sure that you have DEP for essential Windows programs and services only enabled:

Windows 7
  1. Click Start to open System
  2. Right-click Computer, then select Properties
  3. Click Advanced system settings
    If prompted, enter your administrator password or confirmation
  4. Under Performance, click Settings
  5. Select the Data Execution Prevention tab
  6. If necessary, click Turn on DEP for essential Windows programs and services only
  7. Click OK and close System Properties
Older Versions of Windows
  1. Control Panel > System > Advanced > Performance Settings > Data Execution Prevention
  2. Select the Turn on DEP for essential windows programs and services only
  3. Click Apply or OK

If that doesn't help, then try entering the following commands into Windows Command Prompt:

Net stop vss
Net stop swprv
regsvr32 ole32.dll
regsvr32 vss_ps.dll
Vssvc /Register
regsvr32 /i swprv.dll
regsvr32 /i eventcls.dll
regsvr32 es.dll
regsvr32 stdprov.dll
regsvr32 vssui.dll
regsvr32 msxml.dll
regsvr32 msxml3.dll
regsvr32 msxml4.dll

If that doesn't work, then please send our Customer Champions the results of the following commands (cmd.exe):

C:\> vssadmin list providers
C:\> vssadmin list shadows
C:\> vssadmin list writers

Floppy drive light

There is a known issue within Windows where your floppy disk drive's light may blink when a program uses VSS to make a copy of an open file. You can disable the floppy drive from the Windows Device Manager if you'd like to stop the blinking. There's more information about using Device Manager on Microsoft's support site.