Interconnecting computers in a datacenter

1. A method for configuring a datacenter network having a first stage of switches and a second stage of switches, the method comprising:

defining first stage switch groups each comprising at least two first stage switches;

defining second stage switch groups each comprising at least two second stage switches;

for each first stage switch group of a first set of first stage switch groups:

connecting each first stage switch in the first stage switch group to second stage switches in a different respective second stage switch group by assigning a communication link between each first stage switch in the first stage switch group and each second stage switch in its respective second stage switch group;

for each first stage switch group of a second set of first stage switch groups:

assigning a communication link between each first stage switch and only a single second stage switch of each second stage switch group.

2. The method of claim 1 , wherein for each first stage switch group, each switch in the first stage switch group is coupled to a common top-of-rack switch.

3. The method of claim 1 , wherein a number of first stage switch groups in the first set of first stage switch groups is equal to a number of first stage switch groups in the second set of first stage switch groups.

4. The method of claim 1 , wherein defining first stage switch groups comprises assigning an equal number of first stage switches to each of the first stage switch groups.

5. The method of claim 1 , further comprising:

assigning a sequential integer index value to each of the first stage switch groups;

assigning first stage switch groups having odd index values to the first set of first stage switch groups; and

assigning first stage switch groups having even index values to the second set of first stage switch groups.

6. The method of claim 1 , wherein each second stage switch is a configurable optical control switch used to form communication links between first stage switches.

7. The method of claim 6 , further comprising disseminating the communication link assignments to the optical control switches.

8. The method of claim 6 , further comprising defining a third stage of switches, each third stage switch coupled to at least one first stage switch.

9. The method of claim 8 , wherein each third stage switch is a top-of-rack switch coupled to one or more servers.

10. A system having a first stage of switches and a second stage of switches, the system comprising:

at least one first stage switch group each comprising at least two first stage switches; and

at least one second stage switch group each comprising at least two second stage switches, wherein:

for each first stage switch group of a first set of first stage switch groups, each first stage switch in the first stage switch group is connected to second stage switches in a different respective second stage switch group by a communication link is formed between each first stage switch in the first stage switch group and each second stage switch in its respective second stage switch group; and

for each first stage switch group of a second set of first stage switch groups, a communication link is formed between each first stage switch and only a single second stage switch of each second stage switch group.

11. The system of claim 10 , wherein for each first stage switch group, each switch in the first stage switch group is coupled to a common top-of-rack switch.

12. The system of claim 10 , wherein a number of first stage switch groups in the first set of first stage switch groups is equal to a number of first stage switch groups in the second set of first stage switch groups.

13. The system of claim 10 , wherein each first stage switch groups comprises an equal number of first stage switches.

14. The system of claim 10 , wherein:

each of the first stage switch groups is assigned a sequential integer index value;

first stage switch groups having odd index values are assigned to the first set of first stage switch groups; and

first stage switch groups having even index values are assigned to the second set of first stage switch groups.

15. The system of claim 10 , wherein each second stage switch is a configurable optical control switch used to form communication links between first stage switches.

16. The system of claim 10 , further comprising a third stage of switches, each third stage switch coupled to at least one first stage switch.

17. The system of claim 16 , wherein each third stage switch is a top-of-rack switch coupled to one or more servers.