VDI Environments

• Cannot create a snapshot on linked clone VM when the parent VM snapshot is on VMFS 6 datastore and child VM is on vSAN
• You receive the following error in vCenter:

• In vmware.log you see:

VMs that have vmdks shared between vSAN and VMFS6 datastores

• Cannot create a snapshot for the VM. You will see similar errors as above.

Note: The preceding log excerpts are only examples. Date, time, and environmental variables may vary depending on your environment.

VDI Environments
This issue occurs because the parent snapshot resides on a vmfs6 datastore. When using auto deploy tools such as vRA, Horizon View, or any 3rd Party auto-deploy tool the parent snapshot uses the default format for snapshots for that datastore.

VMs that have vmdks shared between vSAN and VMFS6 datastores
VMFS6 datastore is low on space to accommodate the snapshot.

Note: SEsparse is the default format for all snapshots on VMFS-6 datastores.

VDI Environments
To resolve this issue do one of the following:

• Upgrade both vCenter and ESXi to 7.0U2 or later.
• For versions earlier than 7.0U2 do not use vmfs6 for templates.

VMs that have vmdks shared between vSAN and VMFS6 datastores
Add more space to the VMFS6 datastore or migrate the vmdk(s) to another datastore that has more space.

Workaround:

VDI Environments
The workaround for this issue is to either:

• Turn off IO coalescing
• Storage vMotion the child VM off of vSAN and then back.

Note:

• Turning off IO coalescing is accomplished by modifying a configuration option on each host.
• To take effect, VMs must be power-cycled or migrated (vMotion) to other hosts that have the config option set.

To turn off IO coalescing

Impact of turning off IO coalescing:
Disabling IO coalescing can cause IO performance degradation while VM is running from the snapshot. The extent of degradation depends on the individual virtual machine workload. 

The advanced configuration parameters that control IO coalescing are not available through the UI. To make these changes, use the ESXi Shell, PowerCLI, or your preferred API method.

To turn off SEsparse IO coalescing using the ESXi Shell:

1. Log into the ESXi host through SSH as root.
2. Determine if IO coalescing is enabled by running this command:
   
   esxcli system settings advanced list -o /COW/COWEnableIOCoalescing. 
   
   Note: The Int Value will be 1 if it is turned on.
    
3. If it is turned on, turn off IO coalescing by running this command:
   
   esxcli system settings advanced set -i 0 -o /COW/COWEnableIOCoalescing.
    
4. Rerun step 2 to confirm that the "Int Value" has changed to "0"
5. Complete this procedure on all hosts.
6. After all hosts have been configured, enter Maintenance Mode on each host in series, or vMotion all VMs to ensure the new setting takes effect. Alternatively, all VMs can be power-cycled.

To turn off SEsparse IO coalescing using PowerCLI:

1. Refer to Using the vSphere PowerCLI utility to manage your vSphere environment for guidance about PowerCLI.

2. Change the advanced configuration parameter on all hosts.

Get-AdvancedSetting -Entity <hostname> -Name "COW.COWEnableIOCoalescing" | Set-AdvancedSetting -Value 0

3. After all hosts have been configured, enter Maintenance Mode on each host in series, or vMotion all VMs to ensure the new setting takes effect. Alternatively, all VMs can be power-cycled.