How the Datto Windows Agent uses Shadow Storage

Topic

This article explains shadow copies and shadow storage, and how they interact with the Datto Windows Agent backup solutions.

Environment

  • Datto Windows Agent
  • Microsoft Windows (all platforms)

Description

Shadow Copies are native Windows VSS snapshots. Shadow storage is the location that Windows uses to store these snapshots.

The Datto Windows Agent backup process uses VSS snapshots and shadow storage. The amount of shadow storage space required depends on how quickly applications modify data after the backup begins, and how quickly the Datto Windows Agent can copy the data into the backup.

ShadowCopy and the Datto Solution

Datto recommends that you disable the Windows Shadow copy process when using the Datto Windows Agent because of the differences in how these solutions and Microsoft Windows interact with shadow storage space. Windows will fill up the shadow storage space until it is completely full, and then destroy the oldest backup to make room for the newest backup. This can have an adverse effect on the Datto backup solution, because it uses the same storage space for its backups. Once we have written the backup to the destination, the software cleans up its shadow copies.

If you cannot disable Windows Shadow Copy, Datto recommends that you set your shadow storage space to unbounded. This will allow the space to grow as necessary to accommodate backups.

IMPORTANT  Note that if your shadow storage space is unbounded, and the Microsoft provider is enabled, following this step will likely fill your hard drive.

Working with Shadow Storage

The following commands will allow you to manage shadow copies and shadow storage from the Windows Command Prompt. You will need to launch the Command Prompt session as an administrator.

View existing shadow copies:

vssadmin list shadows

View the size of the storage:

vssadmin list shadowstorage

Change the allocated size for your shadow storage:

vssadmin resize shadowstorage /for=<ForVolumeSpec> /on=<OnVolumeSpec> [/maxsize <MaxSizeSpec>]
  • If no value is specified for /maxsize, there is no limit placed on the amount of storage space that can be used

Creating .Shadow Storage

In the event that it does not already exist, you can add Shadow Storage on your protected machine.

vssadmin add shadowstorage

For more information, see Vssadmin add shadowstorage(external article)

Additional Resources