vCenter Server 5.x uses different internal identifiers for datastores than earlier versions of vCenter Server. This change affects the way that you add shared NFS datastores to hosts and can affect upgrades to vCenter Server 5.x.
vCenter Server versions before version 5.0 convert datastore host names to IP addresses. For example, if you mount an NFS datastore by the name \\nfs-datastore\folder, pre-5.0 vCenter Server versions convert the name nfs-datastore to an IP address like 10.23.121.25 before storing it. The original nfs-datastore name is lost.
This conversion of host names to IP addresses causes a problem when DNS load balancing solutions are used with vCenter Server. DNS load balancing solutions themselves replicate data and appear as a single logical datastore. The load balancing happens during the datastore host name-to-IP conversion by resolving the datastore host name to different IP addresses, depending on the load. This load balancing happens outside vCenter Server and is implemented by the DNS server. In vCenter Server versions before version 5.0, features like vMotion do not work with such DNS load balancing solutions because the load balancing causes one logical datastore to appear as several datastores. vCenter Server fails to perform vMotion because it cannot recognize that what it sees as multiple datastores are actually a single logical datastore that is shared between two hosts.
To solve this problem, vCenter Server versions 5.0 and later do not convert datastore names to IP addresses when you add datastores. This enables vCenter Server to recognize a shared datastore, but only if you add the datastore to each host by the same datastore name. For example, vCenter Server does not recognize a datastore as shared between hosts in the following cases.
The datastore is added by IP address to host1 and by hostname to host2.
The datastore is added by hostname to host1, and by hostname.vmware.com to host2.
For vCenter Server to recognize a datastore as shared, you must add the datastore by the same name to every host.
Datastore Names and Upgrades to vCenter Server 5.x
In vCenter Server versions before version 5.0, vCenter Server database stores datastore paths in the old format, as IP addresses. The upgrade to vCenter Server 5.x converts these paths to the new format. If you use a DNS load balancing solution with shared datastores, before you upgrade to vCenter Server 5.x, make sure that every shared datastore is mounted on each of its hosts with the same name.
The upgrade to vCenter Server 5.x might also fail from a lack of sufficient memory if you use a DNS load balancing solution with shared datastores. In a large vCenter Server database, the conversion of datastore paths to the new format can require a large amount of memory. See the VMware Knowledge Base article at http://kb.vmware.com/kb/2015055.