Thare are at least three relevent documents:
Also, since 10.0 and beyond is only supported in a virtualized deployment, ensure that you understand all of the requirements on that front:
Note: Downtime is required
When underlying OS needs to be changed, cop file is needed first to install to upgrade OS before proceeding with normal upgrade
When upgrading from 8.6 to 11.x, instead of using 'disc expansion' COP file, could i not just build new VM with correct specs and then DRS current 8.6 to new VM, then upgrade to 11.x?
Cheers in advance.
No, you need to match the OVA to the CUCM version, you'd need to adjust the settings as required, and once you're on 11.x, do the DRS backup/restore procedure on a fresh 11.x install.
The other option is to use PCD to perform the migration and you don't have to perform any VM changes in your original server.