RDM multi-writer clustered windows

Hello,

I configuring a windows 2016 cluster on two VMs in 6.5 compatibility mode, when adding an existing physical RDM on the second node, error appears that the file can not be opened.

I changed the RDM option to multi-writer and managed to add RDM on the second node.

However, I have another Windows 2008 R2 cluster with VMs in 5.5-mode compatibility in the same VMware environment and meet physical rdm disks in non-shared mode and it works normally.

Why did I need to set up multi-writer?

Thank you.