Patent ID: 8452819

Claim:
A distributed storage data center, comprising: a data center network; a plurality of storage units each coupled to the data center network that collectively store client data for a plurality of clients, wherein the data center network carries general client I/O traffic from the plurality of clients to the plurality of storage units, wherein the general client I/O traffic includes reads from and writes to the client data collectively stored on the plurality of storage units; one or more devices coupled to the data center network, wherein the one or more devices implement a data migration module operable to: initiate migration of data units among the plurality of storage units according to a storage load balancing technique to maintain a balanced distribution of the client data across the plurality of storage units; detect addition of one or more new storage units to the data center network; in response to said detecting the addition of the one or more new storage units to the data center network: block general client I/O traffic to the one or more new storage units on the data center network; initiate migration of data units from each of one or more of the plurality of storage units to the one or more new storage units according to the storage load balancing technique to balance storage load across the plurality of storage units and the one or more new storage units, wherein general client I/O traffic is allowed to go through to the one or more of the plurality of storage units during said migration of data units from the one or more of the plurality of storage units to the one or more new storage units, and wherein general client I/O traffic remains blocked to the one or more new storage units during said migration of data units from the one or more of the plurality of storage units to the one or more new storage units; determine that storage load is balanced across the plurality of storage units and the one or more new storage units; and in response to said determining that storage load is balanced across the plurality of storage units and the one or more new storage units, unblock general client I/O traffic to the one or more new storage units on the data center network.