Hyper-V VSS snapshot import delay

KB ID: 1844
Product: Veeam Backup & Replication
Version: 7.x
Published: 2013-12-18
Last Modified: 2020-08-13
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Challenge

If you backup your VMs using Dell Equallogic hardware VSS provider in some cases data(vhd/vhdx) that we read from VSS snapshot could be inconsistent

Cause

During Hyper-V backup, we execute VSS API call DoSnapshotSet, as soon as it completes, we execute ImportSnapshot VSS API call, without any delay between two API calls.
Apparently Dell VSS hardware provider continues to write some data to VSS snapshot after execution of DoSnapshotSet method(after returning S_OK code), and if we try to immediately import VSS snapshot, we could backup inconsistent data from that VSS snapshot.

Solution

In order to workaround this problem we introduce a timeout/delay between execution of ImportSnapshot VSS API call
Open registry editor on Veeam Backup console
Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Veeam\Veeam Backup and Replication
Create DWORD parameter:
HvDelayBeforeSnapshotImportCompleteSec
Set it to 90 seconds(or more if your hardware VSS provider requires more time).

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