5 1 0:SEP sesam Volume Shadow Copy Service (VSS) for Windows

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Welcome to the latest SEP sesam documentation version 5.1.0 Apollon. For previous documentation version(s), check documentation archive.


By default, SEP sesam uses Microsoft VSS to create volume shadow copies of data for every file system – Path backup of a Windows client. The option Backup with VSS can be disabled/enabled when creating a backup task or in the backup task properties, as described in the section Disabling/enabling VSS-based backup. It is also possible to exclude only specific VSS writers, as described in Manually excluding a VSS writer from backup.

About VSS

Microsoft Volume Shadow Copy Service (VSS) is a Windows service for backing up running applications. VSS coordinates with other VSS-aware applications and services, and creates a shadow copy or snapshot of data for backup purposes. VSS uses a copy-on-write snapshot, allocating a small temporary storage space for it. This does not occupy a lot of space as a snapshot only contains the data that has changed since the snapshot started. Once the snapshot is completed, the temporary storage space is freed up again.

If there are any problems with shadow copies remaining and occupying your disk space, check Microsoft tools Diskshadow and VSSadmin to manage and delete shadow copies.

VSS architecture

The VSS architecture includes the following objects and services:

  • Provider: An operating system object that manages running volumes and create the shadow copies of them on demand as well as coordinates all elements. A VSS Provider is included in Windows installation.
  • Requester: Typically, a VSS-aware backup application (in our case SEP sesam) that sends a snapshot request to the provider. It also communicates with writers to gather system information and to signal writers to prepare their data for backup.
  • Writers: Services that prepare applications for snapshot creation and backup. They ensure that their data is quiescent and in a consistent state. Once the snapshot is created, they let the applications resume.


  • VSS is provided on Windows operating system versions beginning with Windows XP.
  • Even though Windows has a limit of up to 512 shadow copies per volume, a maximum of 64 shadow copies can be maintained. If the restricted total amount of created volumes is exceeded, the VSS backup will fail. Note that the total amount of snapshots also includes snapshots that might be created with another application/for another purpose.
  • Make sure that the minimum required disk space for shadow copy creation is available. Microsoft article Troubleshoot VSS issues provides the following information: For volumes less than 500 megabytes, the minimum is 50 megabytes of free space. For volumes more than 500 megabytes, the minimum is 320 megabytes of free space. It is recommended that least 1 gigabyte of free disk space on each volume if the volume size is more than 1 gigabyte.

SEP sesam backup with VSS

SEP sesam backup with VSS supports copy, full, differential, and incremental backups of the file system, therefore the option Backup with VSS should only be used with the task type Path. All other task types, for example System State, use the required VSS writer by default.

When performing a VSS backup, SEP sesam as a requester requests a backup of the file system data specified in the backup task. VSS writers communicate with running applications and ensure that the data is set to a consistent state and to stay consistent during the shadow copy creation. SEP sesam backs up the selected data immediately after VSS takes a snapshot of the selected data. Once the backup is complete, VSS instructs running applications to resume normal operation. The file system data on the saveset is stored with the original location, e.g., C:\. This enables standard restore of data backed up with VSS. For details, see Standard Restore Procedure.

Ensure that Windows AutoUpdate is disabled during a backup with VSS. If the autoupdate is running while backup with VSS is in progress, it may cause the backup job to fail with WIN32 API error: 21 – The Device is not ready.

Disabling/enabling VSS-based backup

In the Main Selection -> Tasks -> By Clients, select your Windows client and then click the backup task for which you want to change the properties or click New Backup Task if you are creating a new task. After setting the task properties, disable (or enable) the option Backup with VSS. By default, the VSS backup is enabled.

Disabling the VSS option is highly discouraged. Doing so could lead to backup data inconsistency.

Backup with VSS activates all of the available VSS writers. If you want to exclude a specific VSS writer from the backup, proceed as described in Manually excluding a VSS writer from backup.

Manually excluding a VSS writer from backup

Application specific VSS writers are used to coordinate and prepare application data for snapshot creation while it can still be in use. The following Windows software and services support VSS: Hyper-V, SQL Server, Exchange Server, SharePoint, Virtual Server, Active Directory, DHCP, WMI. You can exclude a specific writer from the backup, if it is not needed for your current backup task (e.g., exclude a Hyper-V writer because you have another task dedicated for backing up a Hyper-V system).

You can exclude one or more VSS writers in the same way you exclude data from the backup.

  1. In the Main Selection -> Tasks -> By Clients, select your Windows client and then click the backup task whose properties you want to change, or click New Backup Task if you are creating a new task. The backup task properties window is displayed.
  2. Make sure that the option Backup with VSS is enabled. Then click the browse button next to the fields Source and Exclude list. The Client File View is displayed.
  3. Click the expand/collapse sign next to VSS writers and select the writer(s) you want to exclude from the backup. The excluded writers are listed at the bottom of the Excluded field. Clik OK to confirm your selection.

Changing the temporary storage location for VSS shadow copies

By default, VSS shadow copies (snapshots) are stored at the same location as the original data, for example, drive C has its shadow copy on C, drive D on D, etc. However, you may want to save your temporary VSS shadow copy to a different drive (e.g., one with a greater capacity or to organize all your snapshots in a separate location). In this case, you can change the designated drive for the VSS shadow copies to another storage area location (local drive).

The procedure differs depending on whether you want to change the storage area location on Windows Server OS or Windows Desktop OS.

On Windows Server OS

On Windows Server OS, you can change the designated drive for VSS shadow copies as follows:

  1. Open File Explorer (previously Windows Explorer) and right-click the relevant drive letter for which you want to change the location.
  2. Select Configure Shadow Copies. The new Shadow Copies window appears.
  3. From the Select a volume list, select the drive for which you want to change the location.
  4. Click Settings to open the Settings window for the selected drive.
  5. Set up a new location (local drive) for VSS shadow copies; you can also specify the size of the shadow copy storage.
  6. Click OK to close your session.

On Windows Desktop OS

As an administrator, you can change the location and size of the storage area in the commad prompt by entering the following command:

vssadmin resize shadowstorage /for=<for_drive> /on=<on_drive> /maxsize=<maximum_size>

where for specifies the source volume of the storage, on specifies the drive where the shadow storage will be, and maxsize sets the maximum size of the shadow storage area. For example:

vssadmin resize shadowstorage /for=C: /on=E: /maxsize=15%

For more information on how to use the command, see the Microsoft article Vssadmin resize shadowstorage.

See also

VSS TroubleshootingCreating a Backup TaskBackupAdding a Task to the Task Group

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