VMs stored on vVols may experience a significant stun during the snapshot removal process after the backup session.

Challenge

After backing up a VM stored on vVol with HotAdd, snapshot removal operations stun the VM if the backup proxy server is located on a different ESXi host.

Cause

The snapshot removal process hangs as it waits for the volume unbind on the ESXi host. This issue can occur with any ESXi configuration using vVols on vCenter 6.0 and later versions.

Solution

To solve the issue with the VM stun, you can add a registry key on the backup server that will add a delay between the HotAdd detach and the snapshot removal processes. Note that your Veeam Backup & Replication version must be 9.5 Update 3 (9.5.0.1536) or later.

To add the registry key, do the following:

1. On the Veeam Backup & Replication server, click Start and then click Run.
2. In the Open box, type regedit.
3. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Veeam\Veeam Backup and Replication\.
4. Right-click the policy folder, select New > DWORD (32-bit) Value.
5. Add the REG_DWORD parameter with the name HotaddTimeoutAfterDetachSec 
6. Set the value to 60.

The exact value you need can be determined only by testing. In most cases, 60 seconds has been plenty for VMs to detach the disks before the "Snapshot removal" command was issued. Less may also work. It is possible that in some environments a larger delay may be required.