I have found a bug in Hyper-V Server 2019. This may exist in Server Core 2019, but I've wasted my entire day on this already and do not care to try.
Hyper-V Server 2019 hosts, all identical
Synology NAS running SMB 3, current DSM 6 release
Dynamically Expanding VHDX files on a Synology SMB share - 3TB each. One formatted to ReFS, the other to NTFS
A script is designed to mount the VHDX and Windows Server Backup operations occur on the VHDX
Went to run a one-off backup this morning to the ReFS disk and it wouldn't run. "ERROR - The specified backup location could not be found or is not a supported backup storage location."
Tried to create a NTFS formatted VHDX (assuming it was a ReFS issue) on the HV system, the hypervisors could create the VHDX, could online it, initialise it and create the partition, but could not format it.
Created the VHDX off-machine, moved it over, attempted the backup and it failed with the same error.
Fully patched the HV install to 2021-07, same error
Ran diskpart list disk - OK
Ran diskpart list partition - OK
Ran diskpart list volume - drive mount point (B:) not shown, volume missing
Go to cmd, can browse and search B:\ fine
Go to PowerShell can browser and search B:\ fine
Use Get-Disk, Get-Partition and Get-Volume in PowerShell - All OK, B drive is displayed as expected in PowerShell's WMI calls
Ran wbadmin get disks which can see the disk but gives:
Volumes: There are no volumes on the disk or Windows is unable to retrieve volume information.
Arduously De-installed the following KB's, rebooting after each
It all worked again after the removal of "2021-04 Cumulative Update for Windows Server 2019 for x64-based Systems (KB5001342)"
Installed "2021-03 Cumulative Update for Windows Server 2019 for x64-based Systems (KB5001638)" - all fine
Installed "2021-04 Cumulative Update Preview for Windows Server 2019 for x64-based Systems (KB5001384)" - broken again.
Roll back to 2021-03, all fine again.
It appears that something got into the 2021-04 branch and made it into production which has broken the API for reading the disk information. It is doing this on all of my Hyper-V Server 2019 installs. All of the installs work when rolled back to 2021-03.
All Windows Server 2019 GUI instances that I have are not exhibiting this issue.
A full and more comprehensive write-up can be found at: https://www.c-amie.co.uk/technical/hyper-v-server-2019-cannot-backup-to-or-format-a-vhdx-drive/
Anyone else seen this?