Just found this very interesting article http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1013109 describing a problem with Windows 2008 and ESX 4 virtual hardware version 7.

In short the article states that you might have the disks go offline in a Windows 2008 VM if you

  • Upgrade virtual hardware from version 4 to 7
  • Installing a new VM with virtual hardware 7

There is two ways to get around this (taken from the VMware KB 103109)

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This can be resolved by changing the SAN Automount Policy on the system. See the Microsoft article http://support.microsoft.com/kb/973834 to change the SAN Policy to online.
The SAN policy is defined within the VDS environment of the system and is represented by the following values:
  • VDS_SP_UNKNOWN = 0x0
  • VDS_SP_ONLINE = 0x1
  • VDS_SP_OFFLINE_SHARED = 0x2
  • VDS_SP_OFFLINE = 0x3
On Windows Server 2008 Enterprise and Windows Server 2008 Datacenter, the default SAN policy is VDS_SP_OFFLINE_SHARED. On all other Windows Server 2008 editions, the default SAN policy is VDS_SP_ONLINE.
To query current SAN policy from the command line, start DISKPART and issue a SAN command:
C:\>DISKPART.EXE
DISKPART> san
SAN Policy : Offline Shared

DISKPART> exit

Alternatively, you can set the disk to Online after the hardware version upgrade.
To set the disk to Online:
  1. Log in to your system as an Administrator.
  2. Click Computer Management > Storage > Disk Management.
  3. Right-click the disk and choose Online.