Attempts to enable the multi-writer virtual disk option on an NFS datastore fail

Products

• VMware vSphere ESXi

Issue/Introduction

To configure the multi-writer option on a virtual disk, the disk must be in thick provision eager zeroed format. However, on NFS datastores that do not support vSphere APIs for Array Integration (VAAI), the only available format for virtual disks is thin.

If you use the vSphere Web Client to enable multi-writer on the thin disk that resides on an NFS datastore, the operation fails with the following error message:

Incompatible device backing specified for device '0'

Environment

VMware vSphere ESXi 6.7
VMware vSphere ESXi 6.5
VMware vSphere ESXi 8.0.x
VMware vSphere ESXi 7.0.0

Resolution

1. Create a virtual disk in thick provision eager zeroed format by using the following command:

   vmkfstools -c disk_size[kK|mM|gG] -d eagerzeroedthick disk_location

   For example, vmkfstools -c 2g -d eagerzeroedthick /vmfs/volumes/myDatastore/disk.vmdk

2. To enable Multi Writer flag for sharing a particular disk, do step 2.1 - 2.4 below:
   1. Power off the virtual machine.
   2. In the .vmx file that defines the virtual machine, add an entry similar to:

          scsiX:Y.sharing = "multi-writer"

where X is the controller ID and Y is the disk ID on that controller.
Add this line for each virtual disk that you want to share. For example, to share four disks, the .vmx configuration file entries look like this:

scsi1:0.sharing = "multi-writer"
scsi1:1.sharing = "multi-writer"
scsi1:2.sharing = "multi-writer"
scsi1:3.sharing = "multi-writer"

3. Save the .vmx file
4. Power on the virtual machine.

3. Add the disk to the appropriate VM that resides on the NFS datastore.

Additional Information

https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.storage.doc/GUID-60B9C89A-6638-43FA-A8E3-4DACAC85FC29.html