Relocatable virtual port for accessing external storage

1. A server environment comprising:

a first server having a first host-bus adapter with a first physical port and a first registry for storing a virtual-port identity of a relocatable virtual port in association with said first physical port so that a program running on said first server can access external storage via said first physical port by accessing said relocatable virtual port;

a second server having a second host-bus adapter with a second physical port and a second registry;

a migration manager for migrating said program from said first server to said second server and said virtual port identity from said first registry to said second registry so that said program running on said second server can access external storage via said second physical port by accessing said relocatable virtual port; and

said program, is a virtual server and said relocatable virtual port provides exclusive access to a logical unit of said external storage so that no other virtual server running on said servers can access said logical unit without using said relocatable virtual port.

2. A server environment as recited in claim 1 further comprising:

a controller for deactivating said virtual-port identity as stored in said first registry.

3. A server environment as recited in claim 2 wherein, said migration manager assigns said virtual-port identity.

4. A method comprising:

registering a relocatable virtual port to a first physical port by storing an identity of said relocatable virtual port in a registry of a first host-bus adapter including said first physical port;

accessing external storage via said first physical port by accessing said relocatable virtual port;

registering said relocatable virtual port to a second physical port by storing an identity of said relocatable virtual port in a registry of a second host-bus including said second physical port;

accessing said external storage via said second physical port by accessing said relocatable virtual port;

inactivating the registration of said relocatable virtual port before registering said relocatable virtual port to said second physical port; and

migrating a virtual server from a first server containing said first physical port to a second server containing said second physical port between said accessing, said virtual server performing said accessing.

5. A method as recited in claim 4 further comprising assigning an identity to said relocatable virtual port prior to said registering to said first physical port.

6. A method as recited in claim 5 wherein said identity specifies a bandwidth allocation or a priority or both.

7. A method as recited in claim 4 further comprising dissociating said identity from said first physical port prior to said accessing via said second, physical port.