IBM Support

Unable to remove the last snapshot from the Microsoft Hyper-V GUI

Question & Answer


Question

Why I cannot remove the latest snapshot from Microsoft Hyper-V GUI after a backup using Tivoli Storage Manager for Virtual Environments?

Cause

A Microsoft Hyper-V guest is represented by XML configuration files and the virtual disk(s) used by the guest are files with extension VHDX. In the Microsoft Hyper-V architecture, snapshots (also called checkpoints) can be VSS snapshots or user snapshots. The guest Tivoli Storage Manager Incremental Forever (IFFULL or IFINCR) backups are triggering VSS snapshots.

Starting a snapshot will create a special differential virtual hard disk called the advanced virtual hard disk (AVHDX).

Each VHDX file of the virtual machine will become a parent to an AVHDX file and the virtual machine will read and write data generated after the snapshot from the AVHDX file, while will continue to read only data older than the snapshot from the original VHDX file.

During the next incremental backup, a new AVHDX file is generated to start recording the changes on the disk, while the older AVHDX file is committed in the original VHDX file. At this point, the guest will continue to read only data from the VHDX and will write and read the data changed from the newly generated AHVDX file.

That means that after the initial backup, there will permanently be a AVHDX file for each VHDX file.
With time and depending on the disk activity, the AHVDX will grow with the changes.
That means that regular backups needs to be done to avoid having very big AVHDX files.

Answer

Removing the snapshot is not recommended because by design Tivoli Storage Manager for Virtual Environment - Data Protection for Microsoft Hyper-V will need it to keep track of the changes between the latest backup and the next one.

If the AVHDX file is removed, then the next backup will be a full one.

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Document Information

Modified date:
17 June 2018

UID

swg21690429