VMware ESX Server cannot see existing VMFS3 Volume

I had a problem in one of my DRS/HA Clusters where one ESX 3.0.2 host was unable to see an existing VMFS volume although the volume was in use by other ESX hosts in the cluster, and we confirmed that the SAN LUN zoning was done correctly.

I did have the option in the VI client to add more storage, and then select the LUN, but that would reformat the LUN and I would loose all my existing VM's on that volume.

The fix to this issue was to reset the LUN with "Resignaturing"...

To reset the LUn so it can be presented to the ESX host:

Ensure that no ESX hosts are using or locking the LUN.

In the VI Client, select the ESX host and select the configuration tab
Click on "Advanced Settings"
Select LVM in the left pane
Set LVM.EnableResignature to 1 and click OK
Click "Storage Adapters"
Click "Rescan", then click OK
Click on Storage (SCSI, SAN and NFS)
The volume should now appear as snapshot-xxx
Right click and select "Rename" from the context menu
Click on "Advanced Settings"
Select LVM in the left pane
Set LVM.EnableResignature to 0 and click OK

On the remaining ESX hosts:

Select the ESX host
Select the Configuration tab
Click Storage Adapters
Click Rescan
Click OK
Click on Storage (SCSI, SAN, NFS)
The volume should now appear fine.