The disk is offline because of policy set by an administrator

You have just installed or cloned a VM with Windows 2008 Enterprise or Datacenter or you have upgraded the VM to Virtual Hardware 7 and under Disk Management you get an error message saying:

"the disk is offline because of policy set by an administrator".

This is because, and this is by design, all virtual machine disk files (VMDK) are presented from Virtual hardware 7 (the one of ESX 3.5) to VMs as SAN disks.

At the same time, and this is by design too, Microsoft has changed how SAN disks are handled by its Windows 2008 Enterprise and Datacenter editions.

In fact, on Windows Server 2008 Enterprise and Windows Server 2008 Datacenter (and this is true for R2 too), the default SAN policy is now VDS_SP_OFFLINE_SHARED for all SAN disks except the boot disk.

Having the policy set to Offline Shared means that your SAN disks will be simply offline on startup of your server and if your paging file is on one of this secondary disks it will be unavailable.

Here's the solution to this annoying problem.

What you have to do is first to query the current SAN policy from the command line with DISKPART and issue the following SAN commands:

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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, you have two options to set the disk to Online.

The first one is to log in to your system as an Administrator, click Computer Management > Storage > Disk Management, right-click the disk and choose Online.

The second one is to make a SAN policy change, then select the offline disk, force a clear of its readonly flag 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> ATTRIBUTES DISK CLEAR READONLY

Disk attributes cleared successfully.

DISKPART> attributes disk

Current Read-only State : No

Read-only : No

Boot Disk : No

Pagefile Disk : No

Hibernation File Disk : No

Crashdump Disk : No

Clustered Disk : No

DISKPART> ONLINE DISK

DiskPart successfully onlined the selected disk.

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Once that is done, the drive mounts automagically.