What link costs are

Link costs refers to the relative costs of communicating between data center sites. Link costs are used to determine which grid nodes should provide a requested service.

For example, link cost information is used to determine which LDR services are used to retrieve objects. All else being equal, the service with the lowest link cost is preferred.

In the example shown below, if a client application at data center site two (DC2) retrieves an object that is stored both at data center site one (DC1) and at data center site three, the LDR service at DC1 is responsible for sending the object because the link cost from DC1 to DC2 is 0, which is lower than the link cost from the DC3 site to the DC2 site (25).

Conceptual diagram for link costs between data centers
The table shows example link costs.
Link Link cost Notes
Between physical data center sites 25 (default) Usually a high-speed WAN link exists between sites.
Between logical data center sites 0 Logical data centers at the same physical site connected by a LAN.