Storage Systems Using Write Off-Loading

• US 20090249001A1
• Filed: 03/31/2008
• Published: 10/01/2009
• Est. Priority Date: 03/31/2008
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: ROWSTRON, Anthony, ELNIKETY, Sameh, DONNELLY, Austin, THERESKA, Eno, Narayanan, Dushyanth
• Granted Patent: US 8,074,014 B2
• Time in Patent Office: Days
• US Class Current: 711/161
• CPC Class Codes: G06F 1/3203 Power management, i.e. event-based initiation of a power-saving mode
• CPC Class Codes: G06F 1/3268 Power saving in hard disk drive
• CPC Class Codes: G06F 11/1441 Resetting or repowering
• CPC Class Codes: G06F 11/1471 involving logging of persistent data for recovery
• CPC Class Codes: G06F 11/3433 for load management allocation of a server based on load conditions G06F9/505; load rebalancing G06F9/5083; redistributing the load in a network by a load balancer H04L67/1029
• CPC Class Codes: G06F 11/3485 for I/O devices
• CPC Class Codes: G06F 2201/82 Solving problems relating to consistency
• CPC Class Codes: G06F 3/0625 Power saving in storage systems
• CPC Class Codes: G06F 3/0634 by changing the state or mode of one or more devices
• CPC Class Codes: G06F 3/0689 Disk arrays, e.g. RAID, JBOD
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

Improved storage systems which use write off-loading are described. When a request to store some data in a particular storage location is received, if the particular storage location is unavailable, the data is stored in an alternative location. In an embodiment, the particular storage location may be unavailable because it is powered down or because it is overloaded. The data stored in the alternative location may be subsequently recovered and written to the particular storage location once it becomes available.

Claims

1. A method of storing data comprising:

receiving a request from a client to store data on a first storage device;

determining if defined criteria are met; and

if the defined criteria are met, storing the data on a second storage device and not on the first storage device.

2. A method according to claim 1, wherein determining if defined criteria are met comprises:

determining if the first storage device is powered down.

3. A method according to claim 2, wherein determining if defined criteria are met further comprises:

determining if a previous version of at least a portion of the data is stored a storage device other than the first storage device.

4. A method according to claim 1, wherein determining if defined criteria are met comprises at least one of:

determining if the first storage device is overloaded; and

determining if the first storage location has a higher load than an alternative storage location.

5. A method according to claim 1, wherein storing the data on a second storage device comprises:

selecting a second storage device from a set of storage devices based on load metrics for each of the set of storage devices;

sending a request to store the data to the second storage devices; and

receiving an acknowledgement from the second storage devices confirming that the data has been stored.

6. A method according to claim 5, further comprising:

selecting at least one other storage devices from the set of storage devices based on load metrics for each of the set of storage devices; and

sending the request to store the data to each of the selected storage devices.

7. A method according to claim 1, further comprising:

recovering the data from the second storage devices and storing it on the first storage device.

8. A method according to claim 7, further comprising:

sending a request to delete the data to the second storage device.

9. A method according to claim 1, further comprising:

determining if the first storage device is idle; and

if the first storage device is idle, powering down the first storage device.

10. A method according to claim 9, further comprising:

powering up the first storage device on receipt of a request from a client to read data stored on the first storage device.

11. A method according to claim 1, further comprising:

maintaining a data structure comprising storage locations for data stored on storage devices other than the first storage device.

12. A storage system comprising:

a plurality of storage devices; and

a storage manager associated with a first storage device from the plurality of storage devices,

wherein the storage manager is arranged to;

intercept a write request to the first storage device; and

forward the write request to a storage location on at least one other of the plurality of storage devices if the first storage device is unavailable.

13. A storage system according to claim 12, wherein forwarding the write request to a storage location on at least one other storage device if the first storage device is unavailable comprises at least one of:

forwarding the write request to a storage location on at least one other of the plurality of storage devices if the first storage device is powered down; and

forwarding the write request to a storage location on at least one other of the plurality of storage devices if the first storage device is overloaded.

14. A storage system according to claim 12, wherein the first storage device comprises a volume of disks and wherein the storage location on at least one other of the plurality of storage devices comprises a partition on a second volume of disks.

15. A storage system according to claim 12, further comprising a logger module associated with said storage location, wherein the logger module is arranged to:

receive a write request from the storage manager, the write request comprising data and metadata; and

store the data and the metadata in said storage location.

16. A storage system according to claim 15, wherein said storage location comprises a circular log and wherein the logger module is further arranged, for each write request received, to:

store an epoch identifier associated with the write request and an epoch identifier associated with a previous write request; and

to generate a new epoch identifier at least each time the circular log wraps around a header block in the log.

17. One or more tangible device-readable media with device-executable instructions for performing steps comprising:

receiving a write request to a first storage location, the write request comprising data;

determining if the first storage location is unavailable; and

if the first storage location is unavailable;

selecting at least one alternative storage location; and

forwarding the write request to the at least one alternative storage location.

18. One or more tangible device-readable media according to claim 17, wherein determining if the first storage location is unavailable comprises at least one of:

determining if the first storage location is powered down;

determining if the first storage location is overloaded; and

determining if the first storage location has a higher load than an alternative storage location.

19. One or more tangible device-readable media according to claim 17, wherein selecting at least one alternative storage location comprises:

accessing status data for a plurality of alternative storage locations; and

selecting at least one alternative storage location from the plurality of alternative storage locations based on the status data.

20. One or more tangible device-readable media according to claim 17, further comprising device-executable instructions for performing steps comprising:

when the first storage location is available, accessing said data stored on the at least one alternative storage location; and

storing the data in the first storage location.