Modification of when workloads access data units and/or on which storage devices data units are stored to conserve power

1. A system comprising:

a plurality of storage devices on which a plurality of data units are stored, each data unit stored on one of the storage devices;

a processor; and

a non-transitory computer-readable data storage medium storing computer-executable code executable by the processor to:

correlate a plurality of workloads to the data units with respect to which of the workloads access which of the data units, and when the workloads access the data units;

modify one or more of when the workloads access the data units, and on which of the storage devices the data units are stored, so that at given times the data units stored on a sub-plurality of the storage devices are not being accessed by any workload; and

during each given time, power off the sub-plurality of the storage devices storing the data units that are not being accessed by any workload to conserve power.

2. The system of claim 1 , wherein the computer-executable code is executable by the processor to modify just when the workloads access the data units, without moving any data unit from the storage device on which the data unit is stored.

3. The system of claim 2 , wherein the computer-executable code is executable by the processor to modify just when the workloads access the data units by scheduling execution of the workloads so that the workloads accessing the data units stored on a same storage device are executed during a same time period.

4. The system of claim 3 , wherein when scheduling the execution of the workloads so that the workloads accessing the data units stored on the same storage device are executed during the same time period, the computer-executable code is executable by the processor to realize maximum power conservation regardless of an extent to which the execution of the workloads is reordered.

5. The system of claim 3 , wherein when scheduling the execution of the workloads so that the workloads accessing the data units stored on the same storage device are executed during the same time period, the computer-executable code is executable by the processor to minimize an extent to which the execution of the workloads is reordered although maximum power conservation is not realized.

6. The system of claim 1 , wherein the computer-executable code is executable by the processor to modify just on which of the storage devices the data units are stored, without changing when the workloads access the data units.

7. The system of claim 6 , wherein the computer-executable code is executable by the processor to modify just on which of the storage devices the data units are stored by migrating the data units among the storage devices so that the data units accessed by the workloads during a same time period are stored on a same storage device.

8. The system of claim 7 , wherein when migrating the data units among the storage devices so that the data units accessed by the workloads during the same time period are stored on the same storage device, the computer-executable code is executable by the processor to take into account differences in power efficiency among the storage devices, so that the storage devices that are least power efficient are maximally powered off.

9. The system of claim 7 , wherein when migrating the data units among the storage devices so that the data units accessed by the workloads during the same time period are stored on the same storage device, the computer-executable code is executable by the processor to realize maximum power conservation regardless of a number of the data units migrated.

10. The system of claim 7 , wherein when migrating the data units among the storage devices so that the data units accessed by the workloads during the same time period are stored on the same storage device, the computer-executable code is executable by the processor to minimize a number of the data units that are migrated although maximum power conservation is not realized.

11. The system of claim 1 , wherein each data unit is a separate data file.

12. The system of claim 1 , wherein each data unit is a data block of one of a plurality of data files, each data file comprising a plurality of data blocks, the data blocks of at least one data file stored over more than one of the storage devices.