Folks, I have been facing this issue very random on our Windows server 2016 Virtual machines running on VMware platform. Interestingly, none reported the same to Microsoft (as mentioned by the assigned technician)

Here what we found out, (all credits to  http://www.happysysadm.com/2010/11/disk-is-offline-because-of-policy-set.html)

2 possible caused behind this behavior,

1. How VMware virtual machine disk file presented on a VM,  VMDK files  are presented from Virtual hardware 7 or higher to VMs as SAN disks
2. How Microsoft has changed how SAN disks are handled by Windows 2008 R2 or higher operating systems, default SAN policy is now VDS_SP_OFFLINE_SHARED for all SAN disks except the boot disk. This is to protect the data in a shared disk environment on a cluster. This means shared SAN disks will not be online during the server startup.

There is no clear answer why this random offline state of the disk during reboot. How ever work around for this should be changing the SAN policy to Online all

Run “SAN” at diskpart to verify the SAN policy as shown below

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DISKPART.EXE

DISKPART> san

SAN Policy : Offline Shared

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Once you have verified that the applied policy is Offline Shared, make a SAN policy change, then select the offline disk and bring it online. Follow these steps:

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DISKPART> san policy=OnlineAll

DiskPart successfully changed the SAN policy for the current operating system.

DISKPART> LIST DISK

Disk ### Status Size Free Dyn Gpt

——– ————- ——- ——- — —

Disk 0 Online 40 GB 0 B

* Disk 1 Offline 10 GB 1024 KB

DISKPART> select disk 1

Disk 1 is now the selected disk.

DISKPART> ONLINE DISK

DiskPart successfully onlined the selected disk.

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Reboot the server to verify all disks are online.

Note: Setting this policy on a clustered server with shared disk could cause potential data loss (Ref : https://technet.microsoft.com/en-us/library/gg252636(v=ws.11).aspx )