Topic
This article explains shadow copies and shadow storage, and how they interact with the Datto Endpoint v2 Windows Agent backup solution.
Environment
- Datto Endpoint Backup v2 Windows Agent
- Microsoft Windows
Description
Shadow Copies are native Windows VSS snapshots. Shadow storage is the location that Windows uses to store these snapshots.
The 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 Windows Agent can copy the data into the backup.
Shadow Copy and the Datto Solution
Datto recommends that you disable volume level shadow copies (Previous Versions) when using the Datto Endpoint Backup v2 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 releases the shadow copy and Windows will reclaim that storage as needed.
Microsoft recommends allocating 10% of a volume's size for shadow storage, though this can be adjusted based on the system's needs and disk space. For busy servers or for large volumes, a higher percentage like 15-20% is a good starting point.
If you cannot disable volume level shadow copies because you would like to keep the point in time snapshot functionality, 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 cause the disk to be fully consumed by snapshot data.
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.
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View existing shadow copies:
vssadmin list shadows
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View the size of the storage:
vssadmin list shadowstorage
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Change the allocated size for your shadow storage:
vssadmin resize shadowstorage /For=<SourceVolumeLetter>: /On=<StorageVolumeLetter>: [/MaxSize=<MaxSize>]
EXAMPLE vssadmin resize shadowstorage /For=C: /On=C: /MaxSize=900MB
The maximum size can be set with a set amount of space (MB), a percentage of the storage volume (%), or have no limit (UNBOUNDED).
If no value is specified for /m=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
- Microsoft TechNet: vssadmin resize shadowstorage (external link)
- Microsoft Learn: Volume Shadow Copy Service (VSS) (external link)