When formatting a newly added disk (LUN) to Hyper-V, often you’ll notice the formatting takes forever. Dell EMC therefore advises to disable VAAI on VMware hosts for the same issue, however modern VMware hosts don’t seem to have this problem. Hyper-V however still have this issue. To disable the UNMAP / TRIM from happening, use the following command:

fsutil behavior set DisableDeleteNotify 1

After formatting was performed, you’ll need to re-enable UNMAP / TRIM by issuing the following command:

fsutil behavior set DisableDeleteNotify 0