Modular mass storage system

1. A data storage unit, comprising:

mass storage devices;

a controller configured to access data stored in the mass storage devices;

one or more backplanes, wherein the mass storage devices are coupled to the one or more backplanes;

a duct under at least one of the one or more backplanes; and

an opening configured to vent air from the duct, via the opening, such that the vented air removes heat from mass storage devices downstream of the controller.

2. The data storage unit of claim 1 , wherein:

the vented air combines with air that has removed heat from the controller; and

combined air, comprising the vented air and the air that has removed heat from the controller, flows across respective ones of the mass storage devices located downstream of the controller to remove heat from the respective ones of the mass storage devices located downstream of the controller.

3. The data storage unit of claim 2 , comprising:

a chassis;

an air inlet to the chassis;

an air outlet from the chassis; and

an air passage extending from the air inlet to the air outlet,

wherein the air that has removed heat from the controller flows in the air passage extending from the air inlet to the air outlet.

4. The data storage unit of claim 3 , wherein:

the air flowing in the duct flows in a separate air passage formed at least in part by the duct; and

the separate air passage is located in the chassis below the air passage through which the air that removes heat from the controller flows.

5. The data storage unit of claim 3 , wherein the chassis has a 4 U height.

6. The data storage unit of claim 3 , further comprising:

fans coupled to a rear portion of the chassis.

7. The data storage unit of claim 1 , wherein the duct is formed at least in part by:

a bottom surface of the one of the backplanes; and

a base panel of a chassis of the data storage unit.

8. A data storage system comprising:

a rack; and

a data storage unit mounted in the rack, wherein the data storage unit comprises:

mass storage devices;

a controller configured to access data stored in the mass storage devices;

one or more backplanes, wherein the mass storage devices are coupled to the one or more backplanes;

a duct under at least one of the one or more backplanes; and

an opening configured to vent air from the duct, via the opening, such that the vented air removes heat from mass storage devices downstream of the controller.

9. The data storage system of 8 , comprising:

one or more additional data storage units mounted in the rack; and

a storage controller mounted in the rack,

wherein the storage controller is configured to interface with respective controllers of the data storage unit and the one or more additional data storage units mounted in the rack.

10. The data storage system of claim 8 , wherein the mass storage devices, the controller, the one or more backplanes, the duct, and the opening are included in a chassis of the data storage unit.

11. The data storage system of claim 10 , wherein the chassis has a 4 U height.

12. The data storage system of claim 10 , comprising:

one or more additional data storage units mounted in the rack; and

a storage controller mounted in the rack, wherein the storage controller is configured to interface with respective controllers of the data storage unit and the one or more additional data storage units, wherein:

the data storage unit and the one or more additional data storage units each comprise a chassis having a 4 U height; and

the storage controller comprises a chassis having a 1 U height.

13. The data storage system of claim 8 , wherein the data storage unit comprises:

a chassis;

an air inlet to the chassis;

an air outlet from the chassis; and

an air passage extending from the air inlet to the air outlet,

wherein the air that has removed heat from the controller flows in the air passage extending from the air inlet to the air outlet.

14. The data storage system of claim 13 , wherein:

the air flowing in the duct flows in a separate air passage formed at least in part by the duct; and

the separate air passage is located in the chassis of the data storage unit below the air passage in the data storage unit through which the air that removes heat from the controller flows.

15. The data storage system of claim 13 , further comprising:

fans coupled to a rear portion of the chassis of the data storage unit.

16. The storage system of claim 8 , wherein the duct of the data storage unit is formed at least in part by:

a bottom surface of the one of the backplanes; and

a base panel of a chassis of the data storage unit.

17. A method of cooling a data storage unit, comprising:

flowing air across a controller mounted within a chassis of the data storage unit;

flowing air through an air passage between a backplane within the data storage unit and a chassis of the data storage unit, wherein one or more mass storage devices are coupled to the backplane on a top side of the backplane and the air passage is located under a second side of the backplane, between the backplane and the chassis of the data storage unit; and

venting at least a portion of the air flowing through the air passage through an opening, wherein the vented portion of the air removes heat from other mass storage devices coupled to an additional backplane, wherein the other mass storage devices are on a top side of the additional backplane.

18. The method of claim 17 , wherein the air that flows across the controller flows in an air passage extending from an air inlet of the chassis of the data storage unit to an air outlet of the chassis of the data storage unit.

19. The method of claim 18 , comprising:

causing the air in the air passage and the air in the duct to flow via one or more fans coupled to a rear portion of the chassis.

20. The method of claim 17 , wherein the duct is formed at least in part by:

a bottom surface of the one of the backplanes; and

a base panel of the chassis of the data storage unit.