VMware ESX/ESXi 3.5.0 Update 3 introduced a bug whereby planned or unplanned pathing changes in a multipathed SAN LUN while VMFS3 metadata is being written can cause communication to the SAN LUN(s) to hault, resulting in the loss of virtual disk access (.vmdk) for VMs. The issue is documented in full in VMware KB article 1008130.
A patch is now available in VMware KB article 1006651 which resolves the issue above as well as several others.
For users on ESX/ESX 3.5.0u3, I highly recommend applying this patch as soon as possible.
Jason,
I have no updates via my update manager, any idea when it will be released via it?
Or does one recommend people to download it and browse to the file from within update manager?