RAID controller using capacitor energy source to flush volatile cache data to non-volatile memory during main power outage

• US 7,536,506 B2
• Filed: 09/14/2005
• Issued: 05/19/2009
• Est. Priority Date: 06/21/2004
• Status: Expired due to Fees

• Current Assignee: Dot Hill Systems Corporation (Seagate Technology Holdings Plc)
• Original Assignee: Dot Hill Systems Corporation (Seagate Technology Holdings Plc)
• Inventors: Ashmore, Paul Andrew, Vedder, Rex Weldon, Pecone, Victor Key, Maine, Gene, Lintz, Dwight Oliver
• Primary Examiner(s): Kim; Matt
• Assistant Examiner(s): DUDEK JR, EDWARD J
• Application Number:
  US11/226,825
• Publication Number:
  US 20060015683A1
• Time in Patent Office: 1,343 Days
• Field of Search: 711/114
• US Class Current: 711/114
• 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 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

A write-caching RAID controller is disclosed. The controller includes a CPU that manages transfers of posted-write data from host computers to a volatile memory and transfers of the posted-write data from the volatile memory to storage devices when a main power source is supplying power to the RAID controller. A memory controller flushes the posted-write data from the volatile memory to the non-volatile memory when main power fails, during which time capacitors provide power to the memory controller, volatile memory, and non-volatile memory, but not to the CPU, in order to reduce the energy storage requirements of the capacitors. During main power provision, the CPU programs the memory controller with information needed to perform the flush operation, such as the location and size of the posted-write data in the volatile memory and various flush operation characteristics.

Claims

1. A write-caching redundant array of inexpensive disks (RAID) controller, comprising:

a volatile memory;

a non-volatile memory;

a central processing unit (CPU), for managing transfers of posted-write data from host computers to said volatile memory and transfers of said posted-write data from said volatile memory to storage devices when a main power source is supplying power to the RAID controller;

a memory controller, coupled to said volatile memory and said non-volatile memory, wherein said memory controller is configured to buffer said transfers of said posted-write data from said host computers to said volatile memory and said transfers of said posted-write data from said volatile memory to said storage devices when said main power source is supplying power to the RAID controller, wherein said memory controller, rather than said CPU, is configured to flush said posted-write data from said volatile memory to said non-volatile memory when said main power source fails to supply power to the RAID controller; and

at least one capacitor, coupled to provide power to said memory controller, said volatile memory, and said non-volatile memory when said main power supply fails to supply power to the RAID controller, wherein said CPU is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

2. The RAID controller as recited in claim 1, wherein said memory controller comprises a register for specifying a source location of said posted-write data in said volatile memory, wherein said memory controller flushes said posted-write data from said source location specified in said register to said non-volatile memory.

3. The RAID controller as recited in claim 2, wherein said CPU is configured to program said source location into said register of said memory controller prior to said loss of main power.

4. The RAID controller as recited in claim 2, wherein said memory controller comprises a second register for specifying a destination location of said posted-write data in said non-volatile memory, wherein said memory controller flushes said posted-write data from said source location specified in said first register to said destination location specified in said second register.

5. The RAID controller as recited in claim 4, wherein said CPU is configured to program said destination location into said second register of said memory controller prior to said loss of main power.

6. The RAID controller as recited in claim 1, wherein said posted-write data is comprised in a plurality of non-contiguous regions in said volatile memory.

7. The RAID controller as recited in claim 6, wherein said CPU is configured to program information specifying said plurality of non-contiguous regions into said memory controller prior to said loss of main power.

8. The RAID controller as recited in claim 1, wherein said memory controller comprises an Advanced Technology Attachment (ATA) device interface for writing said posted-write data to said non-volatile memory.

9. The RAID controller as recited in claim 1, further comprising:

a storage device interface, coupled to said memory controller, for communicating with said storage devices;

wherein said memory controller is configured to transfer said posted-write data from said volatile memory to said storage device interface when said main power source is supplying power to the RAID controller.

10. The RAID controller as recited in claim 9, wherein said storage device interface is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

11. The RAID controller as recited in claim 1, further comprising:

a host interface, coupled to said memory controller, for communicating with said host computers;

wherein said memory controller is configured to transfer said posted-write data from said host interface to said volatile memory when said main power source is supplying power to the RAID controller.

12. The RAID controller as recited in claim 11, wherein said host interface is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

13. The RAID controller as recited in claim 1, further comprising:

a power manager, coupled to said memory controller, configured to detect said loss of main power, and to signal said memory controller to flush said posted-write data from said volatile memory to said non-volatile memory in response thereto.

14. The RAID controller as recited in claim 13, wherein said power manager is configured to detect said memory controller has completed flushing said posted-write data from said volatile memory to said non-volatile memory, and to responsively signal said memory controller to place said volatile memory into a self-refresh mode.

15. The RAID controller as recited in claim 13, wherein said memory controller is configured to indicate to said power manager whether said memory controller is presently flushing said posted-write data from said volatile memory to said non-volatile memory.

16. The RAID controller as recited in claim 15, wherein said memory controller is further configured to indicate to said power manager whether an error occurred when said memory controller attempted to flush said posted-write data from said volatile memory to said non-volatile memory.

17. The RAID controller as recited in claim 13, wherein said power manager is configured to cause said at least one capacitor to cease supplying power to said non-volatile memory and said memory controller after said memory controller has completed flushing said posted-write data from said volatile memory to said non-volatile memory.

18. The RAID controller as recited in claim 1, wherein said non-volatile memory comprises FLASH memory.

19. The RAID controller as recited in claim 18, wherein said FLASH memory comprises NAND FLASH memory.

20. The RAID controller as recited in claim 1, wherein said non-volatile memory comprises an ATA interface controller.

21. The RAID controller as recited in claim 1, wherein said non-volatile memory comprises a plurality of FLASH memory devices configured in parallel to concurrently receive said posted-write data from said memory controller.

22. The RAID controller as recited in claim 1, wherein said non-volatile memory comprises a non-volatile random access memory (NVRAM).

23. The RAID controller as recited in claim 1, wherein said non-volatile memory comprises a disk drive.

24. The RAID controller as recited in claim 1, wherein said non-volatile memory is removable from the RAID controller, wherein said memory controller refrains from flushing said posted-write data from said volatile memory if said non-volatile memory is not present.

25. The RAID controller as recited in claim 1, wherein said at least one capacitor comprises an Aerogel carbon material.

26. The RAID controller as recited in claim 1, wherein a maximum energy storage capacity of said at least one capacitor is less than 1000 Joules.

27. The RAID controller as recited in claim 1, wherein said memory controller is configured to flush said posted-write data from said volatile memory to said non-volatile memory at an aggregate rate of at least 8 Megabytes/second when said at least one capacitor provides power to the RAID controller.

28. The RAID controller as recited in claim 1, wherein the RAID controller consumes on average less than one Joule per Megabyte to flush said posted-write data from said volatile memory to said non-volatile memory when said at least one capacitor provides power to the RAID controller.

29. The RAID controller as recited in claim 1, wherein the RAID controller consumes on average less than 10 Watts to flush said posted-write data from said volatile memory to said non-volatile memory when said at least one capacitor provides power to the RAID controller.

30. The RAID controller as recited in claim 1, wherein the RAID controller consumes on average more than 20 Watts when said CPU is managing said transfers of said posted-write data from said host computers to said volatile memory and transfers of said posted-write data from said volatile memory to said storage devices when a main power source is supplying power to the RAID controller.

31. The RAID controller as recited in claim 1, wherein said memory controller is configured to restore said posted-write data from said non-volatile memory to said volatile memory when said main power source resumes supplying power to the RAID controller.

32. The RAID controller as recited in claim 31, wherein said memory controller is configured to forego restoring said posted-write data from said non-volatile memory to said volatile memory when said main power source resumes supplying power to the RAID controller, if said at least one capacitor continued to supply power to said volatile memory until said main power source resumed supplying power to the RAID controller.

33. The RAID controller as recited in claim 1, wherein said memory controller comprises a register for specifying an indicator, wherein said memory controller is configured to flush said posted-write data from said volatile memory to said non-volatile memory when said main power source fails to supply power to the RAID controller, only if said indicator is a predetermined value.

34. The RAID controller as recited in claim 33, wherein said CPU is configured to program said indicator prior to said loss of main power.

35. The RAID controller as recited in claim 1, wherein said memory controller comprises a register for indicating whether said memory controller is flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said register is readable by said CPU when said main power source resumes supplying power to the RAID controller.

36. The RAID controller as recited in claim 1, wherein said memory controller comprises a register writeable to cause said memory controller to abort flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said register is writeable by said CPU when said main power source resumes supplying power to the RAID controller.

37. The RAID controller as recited in claim 1, wherein said memory controller is configured to write to said non-volatile memory information indicating results of said flushing said posted-write data from said volatile memory to said non-volatile memory when said main power source fails to supply power to the RAID controller.

38. The RAID controller as recited in claim 37, wherein said information comprises a predetermined signature.

39. The RAID controller as recited in claim 37, wherein said information comprises an indication of whether said flushing completed successfully or with an error.

40. The RAID controller as recited in claim 37, wherein said information comprises a cyclic redundancy code computation of said posted-write data.

41. The RAID controller as recited in claim 37, wherein said memory controller comprises a register for specifying an indicator, wherein said memory controller is configured to write to said non-volatile memory said information only if said indicator is a predetermined value.

42. The RAID controller as recited in claim 41, wherein said CPU is configured to program said indicator prior to said loss of main power.

43. A method for preserving posted-write data in a write-caching redundant array of inexpensive disks (RAID) controller, the method comprising:

supplying power, by at least one capacitor, to a volatile memory, a non-volatile memory, and a memory controller of the RAID controller, in response to a loss of main power to the RAID controller;

foregoing supplying power, by the at least one capacitor, to a central processing unit (CPU) of the RAID controller, in response to the loss of main power to the RAID controller, wherein the CPU manages transfers of the posted-write data from host computers to the volatile memory and transfers of the posted-write data from the volatile memory to storage devices when main power is being supplied to the RAID controller prior to the loss thereof, wherein the memory controller buffers the transfers of the posted-write data from the host computers to the volatile memory and the transfers of the posted-write data from the volatile memory to the storage devices when the main power is being supplied to the RAID controller prior to the loss thereof;

flushing posted-write data, by the memory controller rather than by the CPU, from the volatile memory to the non-volatile memory, in response to the loss of main power.

44. The method as recited in claim 43, further comprising:

determining whether the posted-write data in the volatile memory is still valid when the main power is restored;

determining whether said flushing is still in progress; and

aborting said flushing if the posted-write data in the volatile memory is still valid and said flushing is still in progress.

45. The method as recited in claim 44, further comprising:

determining whether a voltage of the at least one capacitor is above a predetermined threshold; and

said aborting said flushing, only if the voltage of the at least one capacitor is above the predetermined threshold.

46. The method as recited in claim 43, further comprising:

determining whether said flushing failed; and

failing over to a redundant RAID controller if said flushing failed.

47. The method as recited in claim 43, further comprising:

programming, by the CPU, the memory controller with a location of the posted-write data in the volatile memory prior to said flushing.

48. The method as recited in claim 43, further comprising:

foregoing supplying power, by the at least one capacitor, to the memory controller and the non-volatile memory, after said flushing.

49. The method as recited in claim 43, further comprising:

placing the volatile memory into a self refresh mode, after said flushing.

50. The method as recited in claim 43, further comprising:

restoring the posted-write data from the non-volatile memory to the volatile memory, after a restoration of main power.

51. The method as recited in claim 50, further comprising:

said restoring the posted-write data from the non-volatile memory to the volatile memory, after a restoration of main power, only if the posted-write data in the volatile memory is no longer valid.

52. The method as recited in claim 43, wherein the at least one capacitor comprises an Aerogel carbon material.

53. The method as recited in claim 43, further comprising:

writing information specifying results of said flushing, by the memory controller, to a predetermined location in the non-volatile memory.

54. A write-caching redundant array of inexpensive disks (RAID) controller, comprising:

a volatile memory;

a non-volatile memory;

a central processing unit (CPU), for managing transfers of posted-write data from host computers to said volatile memory and transfers of said posted-write data from said volatile memory to storage devices when a main power source is supplying power to the RAID controller, wherein said CPU is configured to program a source location into a register of a memory controller prior to a loss of main power;

the memory controller, coupled to said volatile memory and said non-volatile memory, wherein said memory controller is configured to buffer said transfers of said posted-write data from said host computers to said volatile memory and said transfers of said posted-write data from said volatile memory to said storage devices when said main power source is supplying power to the RAID controller, wherein said memory controller, rather than said CPU, is configured to flush said posted-write data from said volatile memory to said non-volatile memory when said main power source fails to supply power to the RAID controller, wherein said memory controller comprises said register for specifying said source location of said posted-write data in said volatile memory, wherein said memory controller flushes said posted-write data from said source location specified in said register to said non-volatile memory; and

at least one capacitor, coupled to provide power to said memory controller, said volatile memory, and said non-volatile memory when said main power supply fails to supply power to the RAID controller, wherein said CPU is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

55. The RAID controller as recited in claim 54, further comprising:

a storage device interface, coupled to said memory controller, for communicating with said storage devices;

wherein said memory controller is configured to transfer said posted-write data from said volatile memory to said storage device interface when said main power source is supplying power to the RAID controller.

56. The RAID controller as recited in claim 55, wherein said storage device interface is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

57. The RAID controller as recited in claim 54, further comprising:

a host interface, coupled to said memory controller, for communicating with said host computers;

wherein said memory controller is configured to transfer said posted-write data from said host interface to said volatile memory when said main power source is supplying power to the RAID controller.

58. The RAID controller as recited in claim 57, wherein said host interface is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

59. The RAID controller as recited in claim 54, further comprising:

a power manager, coupled to said memory controller, configured to detect said loss of main power, and to signal said memory controller to flush said posted-write data from said volatile memory to said non-volatile memory in response thereto.

60. The RAID controller as recited in claim 59, wherein said power manager is configured to detect said memory controller has completed flushing said posted-write data from said volatile memory to said non-volatile memory, and to responsively signal said memory controller to place said volatile memory into a self-refresh mode.

61. The RAID controller as recited in claim 59, wherein said memory controller is configured to indicate to said power manager whether said memory controller is presently flushing said posted-write data from said volatile memory to said non-volatile memory.

62. The RAID controller as recited in claim 61, wherein said memory controller is further configured to indicate to said power manager whether an error occurred when said memory controller attempted to flush said posted-write data from said volatile memory to said non-volatile memory.

63. The RAID controller as recited in claim 59, wherein said power manager is configured to cause said at least one capacitor to cease supplying power to said non-volatile memory and said memory controller after said memory controller has completed flushing said posted-write data from said volatile memory to said non-volatile memory.

64. The RAID controller as recited in claim 54, wherein said non-volatile memory is removable from the RAID controller, wherein said memory controller refrains from flushing said posted-write data from said volatile memory if said non-volatile memory is not present.

65. The RAID controller as recited in claim 54, wherein said at least one capacitor comprises an Aerogel carbon material.

66. The RAID controller as recited in claim 54, wherein a maximum energy storage capacity of said at least one capacitor is less than 1000 Joules.

67. The RAID controller as recited in claim 54, wherein said memory controller is configured to flush said posted-write data from said volatile memory to said non-volatile memory at an aggregate rate of at least 8 Megabytes/second when said at least one capacitor provides power to the RAID controller.

68. The RAID controller as recited in claim 54, wherein the RAID controller consumes on average less than one Joule per Megabyte to flush said posted-write data from said volatile memory to said non-volatile memory when said at least one capacitor provides power to the RAID controller.

69. The RAID controller as recited in claim 54, wherein the RAID controller consumes on average less than 10 Watts to flush said posted-write data from said volatile memory to said non-volatile memory when said at least one capacitor provides power to the RAID controller.

70. The RAID controller as recited in claim 54, wherein the RAID controller consumes on average more than 20 Watts when said CPU is managing said transfers of said posted-write data from said host computers to said volatile memory and transfers of said posted-write data from said volatile memory to said storage devices when a main power source is supplying power to the RAID controller.

71. The RAID controller as recited in claim 54, wherein said memory controller is configured to restore said posted-write data from said non-volatile memory to said volatile memory when said main power source resumes supplying power to the RAID controller.

72. The RAID controller as recited in claim 71, wherein said memory controller is configured to forego restoring said posted-write data from said non-volatile memory to said volatile memory when said main power source resumes supplying power to the RAID controller, if said at least one capacitor continued to supply power to said volatile memory until said main power source resumed supplying power to the RAID controller.

73. The RAID controller as recited in claim 54, wherein said memory controller comprises a register for specifying an indicator, wherein said memory controller is configured to flush said posted-write data from said volatile memory to said non-volatile memory when said main power source fails to supply power to the RAID controller, only if said indicator is a predetermined value.

74. The RAID controller as recited in claim 73, wherein said CPU is configured to program said indicator prior to said loss of main power.

75. The RAID controller as recited in claim 54, wherein said memory controller comprises a register for indicating whether said memory controller is flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said register is readable by said CPU when said main power source resumes supplying power to the RAID controller.

76. The RAID controller as recited in claim 54, wherein said memory controller comprises a register writeable to cause said memory controller to abort flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said register is writeable by said CPU when said main power source resumes supplying power to the RAID controller.

77. A write-caching redundant array of inexpensive disks (RAID) controller, comprising:

a volatile memory;

a non-volatile memory;

a central processing unit (CPU), for managing transfers of posted-write data from host computers to said volatile memory and transfers of said posted-write data from said volatile memory to storage devices when a main power source is supplying power to the RAID controller, wherein said CPU is configured to program a source location into a first register of a memory controller and program a destination location into a second register of said memory controller prior to a loss of main power;

a memory controller, coupled to said volatile memory and said non-volatile memory, wherein said memory controller is configured to buffer said transfers of said posted-write data from said host computers to said volatile memory and said transfers of said posted-write data from said volatile memory to said storage devices when said main power source is supplying power to the RAID controller, wherein said memory controller, rather than said CPU, is configured to flush said posted-write data from said volatile memory to said non-volatile memory when said main power source fails to supply power to the RAID controller, wherein said memory controller comprises said first register for specifying said source location of said posted-write data in said volatile memory and said second register for specifying said destination location of said posted-write data in said non-volatile memory, wherein said memory controller flushes said posted-write data from said source location specified in said first register to said destination location specified in said second register in said non-volatile memory; and

at least one capacitor, coupled to provide power to said memory controller, said volatile memory, and said non-volatile memory when said main power supply fails to supply power to the RAID controller, wherein said CPU is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

78. The RAID controller as recited in claim 77, further comprising:

a storage device interface, coupled to said memory controller, for communicating with said storage devices;

wherein said memory controller is configured to transfer said posted-write data from said volatile memory to said storage device interface when said main power source is supplying power to the RAID controller.

79. The RAID controller as recited in claim 78, wherein said storage device interface is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

80. The RAID controller as recited in claim 77, further comprising:

a host interface, coupled to said memory controller, for communicating with said host computers;

wherein said memory controller is configured to transfer said posted-write data from said host interface to said volatile memory when said main power source is supplying power to the RAID controller.

81. The RAID controller as recited in claim 80, wherein said host interface is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

82. The RAID controller as recited in claim 77, further comprising:

a power manager, coupled to said memory controller, configured to detect said loss of main power, and to signal said memory controller to flush said posted-write data from said volatile memory to said non-volatile memory in response thereto.

83. The RAID controller as recited in claim 82, wherein said power manager is configured to detect said memory controller has completed flushing said posted-write data from said volatile memory to said non-volatile memory, and to responsively signal said memory controller to place said volatile memory into a self-refresh mode.

84. The RAID controller as recited in claim 82, wherein said memory controller is configured to indicate to said power manager whether said memory controller is presently flushing said posted-write data from said volatile memory to said non-volatile memory.

85. The RAID controller as recited in claim 84, wherein said memory controller is further configured to indicate to said power manager whether an error occurred when said memory controller attempted to flush said posted-write data from said volatile memory to said non-volatile memory.

86. The RAID controller as recited in claim 82, wherein said power manager is configured to cause said at least one capacitor to cease supplying power to said non-volatile memory and said memory controller after said memory controller has completed flushing said posted-write data from said volatile memory to said non-volatile memory.

87. The RAID controller as recited in claim 77, wherein said non-volatile memory is removable from the RAID controller, wherein said memory controller refrains from flushing said posted-write data from said volatile memory if said non-volatile memory is not present.

88. The RAID controller as recited in claim 77, wherein said at least one capacitor comprises an Aerogel carbon material.

89. The RAID controller as recited in claim 77, wherein a maximum energy storage capacity of said at least one capacitor is less than 1000 Joules.

90. The RAID controller as recited in claim 77, wherein said memory controller is configured to flush said posted-write data from said volatile memory to said non-volatile memory at an aggregate rate of at least 8 Megabytes/second when said at least one capacitor provides power to the RAID controller.

91. The RAID controller as recited in claim 77, wherein the RAID controller consumes on average less than one Joule per Megabyte to flush said posted-write data from said volatile memory to said non-volatile memory when said at least one capacitor provides power to the RAID controller.

92. The RAID controller as recited in claim 77, wherein the RAID controller consumes on average less than 10 Watts to flush said posted-write data from said volatile memory to said non-volatile memory when said at least one capacitor provides power to the RAID controller.

93. The RAID controller as recited in claim 77, wherein the RAID controller consumes on average more than 20 Watts when said CPU is managing said transfers of said posted-write data from said host computers to said volatile memory and transfers of said posted-write data from said volatile memory to said storage devices when a main power source is supplying power to the RAID controller.

94. The RAID controller as recited in claim 77, wherein said memory controller is configured to restore said posted-write data from said non-volatile memory to said volatile memory when said main power source resumes supplying power to the RAID controller.

95. The RAID controller as recited in claim 94, wherein said memory controller is configured to forego restoring said posted-write data from said non-volatile memory to said volatile memory when said main power source resumes supplying power to the RAID controller, if said at least one capacitor continued to supply power to said volatile memory until said main power source resumed supplying power to the RAID controller.

96. The RAID controller as recited in claim 77, wherein said memory controller comprises a register for specifying an indicator, wherein said memory controller is configured to flush said posted-write data from said volatile memory to said non-volatile memory when said main power source fails to supply power to the RAID controller, only if said indicator is a predetermined value.

97. The RAID controller as recited in claim 96, wherein said CPU is configured to program said indicator prior to said loss of main power.

98. The RAID controller as recited in claim 77, wherein said memory controller comprises a register for indicating whether said memory controller is flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said register is readable by said CPU when said main power source resumes supplying power to the RAID controller.

99. The RAID controller as recited in claim 77, wherein said memory controller comprises a register writeable to cause said memory controller to abort flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said register is writeable by said CPU when said main power source resumes supplying power to the RAID controller.

100. A write-caching redundant array of inexpensive disks (RAID) controller, comprising:

a volatile memory;

a non-volatile memory;

a central processing unit (CPU), for managing transfers of posted-write data from host computers to said volatile memory and transfers of said posted-write data from said volatile memory to storage devices when a main power source is supplying power to the RAID controller, wherein said posted-write data is comprised in a plurality of non-contiguous regions in said volatile memory, wherein said CPU is configured to program information specifying said plurality of non-contiguous regions into a memory controller prior to said loss of main power;

the memory controller, coupled to said volatile memory and said non-volatile memory, wherein said memory controller is configured to buffer said transfers of said posted-write data from said host computers to said volatile memory and said transfers of said posted-write data from said volatile memory to said storage devices when said main power source is supplying power to the RAID controller, wherein said memory controller, rather than said CPU, is configured to flush said posted-write data from said volatile memory to said non-volatile memory when said main power source fails to supply power to the RAID controller; and

at least one capacitor, coupled to provide power to said memory controller, said volatile memory, and said non-volatile memory when said main power supply fails to supply power to the RAID controller, wherein said CPU is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

101. The RAID controller as recited in claim 100, further comprising:

a storage device interface, coupled to said memory controller, for communicating with said storage devices;

wherein said memory controller is configured to transfer said posted-write data from said volatile memory to said storage device interface when said main power source is supplying power to the RAID controller.

102. The RAID controller as recited in claim 101 wherein said storage device interface is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

103. The RAID controller as recited in claim 100, further comprising:

a host interface, coupled to said memory controller, for communicating with said host computers;

wherein said memory controller is configured to transfer said posted-write data from said host interface to said volatile memory when said main power source is supplying power to the RAID controller.

104. The RAID controller as recited in claim 103, wherein said host interface is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

105. The RAID controller as recited in claim 100, further comprising:

a power manager, coupled to said memory controller, configured to detect said loss of main power, and to signal said memory controller to flush said posted-write data from said volatile memory to said non-volatile memory in response thereto.

106. The RAID controller as recited in claim 105, wherein said power manager is configured to detect said memory controller has completed flushing said posted-write data from said volatile memory to said non-volatile memory, and to responsively signal said memory controller to place said volatile memory into a self-refresh mode.

107. The RAID controller as recited in claim 105, wherein said memory controller is configured to indicate to said power manager whether said memory controller is presently flushing said posted-write data from said volatile memory to said non-volatile memory.

108. The RAID controller as recited in claim 107, wherein said memory controller is further configured to indicate to said power manager whether an error occurred when said memory controller attempted to flush said posted-write data from said volatile memory to said non-volatile memory.

109. The RAID controller as recited in claim 105, wherein said power manager is configured to cause said at least one capacitor to cease supplying power to said non-volatile memory and said memory controller after said memory controller has completed flushing said posted-write data from said volatile memory to said non-volatile memory.

110. The RAID controller as recited in claim 100, wherein said non-volatile memory is removable from the RAID controller, wherein said memory controller refrains from flushing said posted-write data from said volatile memory if said non-volatile memory is not present.

111. The RAID controller as recited in claim 100, wherein said at least one capacitor comprises an Aerogel carbon material.

112. The RAID controller as recited in claim 100, wherein a maximum energy storage capacity of said at least one capacitor is less than 1000 Joules.

113. The RAID controller as recited in claim 100, wherein said memory controller is configured to flush said posted-write data from said volatile memory to said non-volatile memory at an aggregate rate of at least 8 Megabytes/second when said at least one capacitor provides power to the RAID controller.

114. The RAID controller as recited in claim 100, wherein the RAID controller consumes on average less than one Joule per Megabyte to flush said posted-write data from said volatile memory to said non-volatile memory when said at least one capacitor provides power to the RAID controller.

115. The RAID controller as recited in claim 100, wherein the RAID controller consumes on average less than 10 Watts to flush said posted-write data from said volatile memory to said non-volatile memory when said at least one capacitor provides power to the RAID controller.

116. The RAID controller as recited in claim 100, wherein the RAID controller consumes on average more than 20 Watts when said CPU is managing said transfers of said posted-write data from said host computers to said volatile memory and transfers of said posted-write data from said volatile memory to said storage devices when a main power source is supplying power to the RAID controller.

117. The RAID controller as recited in claim 100, wherein said memory controller is configured to restore said posted-write data from said non-volatile memory to said volatile memory when said main power source resumes supplying power to the RAID controller.

118. The RAID controller as recited in claim 117, wherein said memory controller is configured to forego restoring said posted-write data from said non-volatile memory to said volatile memory when said main power source resumes supplying power to the RAID controller, if said at least one capacitor continued to supply power to said volatile memory until said main power source resumed supplying power to the RAID controller.

119. The RAID controller as recited in claim 100, wherein said memory controller comprises a register for specifying an indicator, wherein said memory controller is configured to flush said posted-write data from said volatile memory to said non-volatile memory when said main power source fails to supply power to the RAID controller, only if said indicator is a predetermined value.

120. The RAID controller as recited in claim 119, wherein said CPU is configured to program said indicator prior to said loss of main power.

121. The RAID controller as recited in claim 100, wherein said memory controller comprises a register for indicating whether said memory controller is flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said register is readable by said CPU when said main power source resumes supplying power to the RAID controller.

122. The RAID controller as recited in claim 100, wherein said memory controller comprises a register writeable to cause said memory controller to abort flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said register is writeable by said CPU when said main power source resumes supplying power to the RAID controller.

123. A write-caching redundant array of inexpensive disks (RAID) controller, comprising:

a volatile memory;

a non-volatile memory;

a central processing unit (CPU), for managing transfers of posted-write data from host computers to said volatile memory and transfers of said posted-write data from said volatile memory to storage devices when a main power source is supplying power to the RAID controller;

a memory controller, coupled to said volatile memory and said non-volatile memory, wherein said memory controller is configured to buffer said transfers of said posted-write data from said host computers to said volatile memory and said transfers of said posted-write data from said volatile memory to said storage devices when said main power source is supplying power to the RAID controller, wherein said memory controller, rather than said CPU, is configured to flush said posted-write data from said volatile memory to said non-volatile memory when said main power source fails to supply power to the RAID controller, wherein said memory controller is configured to indicate to a power manager whether said memory controller is presently flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said memory controller is further configured to indicate to said power manager whether an error occurred when said memory controller attempted to flush said posted-write data from said volatile memory to said non-volatile memory;

at least one capacitor, coupled to provide power to said memory controller, said volatile memory, and said non-volatile memory when said main power supply fails to supply power to the RAID controller, wherein said CPU is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller; and

the power manager, coupled to said memory controller, configured to detect said loss of main power, and to signal said memory controller to flush said posted-write data from said volatile memory to said non-volatile memory in response thereto.

124. The RAID controller as recited in claim 123, further comprising:

a storage device interface, coupled to said memory controller, for communicating with said storage devices;

wherein said memory controller is configured to transfer said posted-write data from said volatile memory to said storage device interface when said main power source is supplying power to the RAID controller.

125. The RAID controller as recited in claim 124, wherein said storage device interface is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

126. The RAID controller as recited in claim 123, further comprising:

a host interface, coupled to said memory controller, for communicating with said host computers;

wherein said memory controller is configured to transfer said posted-write data from said host interface to said volatile memory when said main power source is supplying power to the RAID controller.

127. The RAID controller as recited in claim 126, wherein said host interface is excluded from receiving power from said at least one capacitor when said main power supply fails to supply power to the RAID controller.

128. The RAID controller as recited in claim 123, wherein said power manager is configured to detect said memory controller has completed flushing said posted-write data from said volatile memory to said non-volatile memory, and to responsively signal said memory controller to place said volatile memory into a self-refresh mode.

129. The RAID controller as recited in claim 123, wherein said power manager is configured to cause said at least one capacitor to cease supplying power to said non-volatile memory and said memory controller after said memory controller has completed flushing said posted-write data from said volatile memory to said non-volatile memory.

130. The RAID controller as recited in claim 123, wherein said non-volatile memory is removable from the RAID controller, wherein said memory controller refrains from flushing said posted-write data from said volatile memory if said non-volatile memory is not present.

131. The RAID controller as recited in claim 123, wherein said at least one capacitor comprises an Aerogel carbon material.

132. The RAID controller as recited in claim 123, wherein a maximum energy storage capacity of said at least one capacitor is less than 1000 Joules.

133. The RAID controller as recited in claim 123, wherein said memory controller is configured to flush said posted-write data from said volatile memory to said non-volatile memory at an aggregate rate of at least 8 Megabytes/second when said at least one capacitor provides power to the RAID controller.

134. The RAID controller as recited in claim 123, wherein the RAID controller consumes on average less than one Joule per Megabyte to flush said posted-write data from said volatile memory to said non-volatile memory when said at least one capacitor provides power to the RAID controller.

135. The RAID controller as recited in claim 123, wherein the RAID controller consumes on average less than 10 Watts to flush said posted-write data from said volatile memory to said non-volatile memory when said at least one capacitor provides power to the RAID controller.

136. The RAID controller as recited in claim 123, wherein the RAID controller consumes on average more than 20 Watts when said CPU is managing said transfers of said posted-write data from said host computers to said volatile memory and transfers of said posted-write data from said volatile memory to said storage devices when a main power source is supplying power to the RAID controller.

137. The RAID controller as recited in claim 123, wherein said memory controller is configured to restore said posted-write data from said non-volatile memory to said volatile memory when said main power source resumes supplying power to the RAID controller.

138. The RAID controller as recited in claim 137, wherein said memory controller is configured to forego restoring said posted-write data from said non-volatile memory to said volatile memory when said main power source resumes supplying power to the RAID controller, if said at least one capacitor continued to supply power to said volatile memory until said main power source resumed supplying power to the RAID controller.

139. The RAID controller as recited in claim 123, wherein said memory controller comprises a register for specifying an indicator, wherein said memory controller is configured to flush said posted-write data from said volatile memory to said non-volatile memory when said main power source fails to supply power to the RAID controller, only if said indicator is a predetermined value.

140. The RAID controller as recited in claim 139, wherein said CPU is configured to program said indicator prior to said loss of main power.

141. The RAID controller as recited in claim 123, wherein said memory controller comprises a register for indicating whether said memory controller is flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said register is readable by said CPU when said main power source resumes supplying power to the RAID controller.

142. The RAID controller as recited in claim 123, wherein said memory controller comprises a register writeable to cause said memory controller to abort flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said register is writeable by said CPU when said main power source resumes supplying power to the RAID controller.

143. A method for preserving posted-write data in a write-caching redundant array of inexpensive disks (RAID) controller, the method comprising:

supplying power, by at least one capacitor, to a volatile memory, a non-volatile memory, and a memory controller of the RAID controller, in response to a loss of main power to the RAID controller, wherein said memory controller comprises a register for specifying a source location of said posted-write data in said volatile memory, wherein said memory controller flushes said posted-write data from said source location specified in said register to said non-volatile memory;

foregoing supplying power, by the at least one capacitor, to a central processing unit (CPU) of the RAID controller, in response to the loss of main power to the RAID controller, wherein the CPU manages transfers of the posted-write data from host computers to the volatile memory and transfers of the posted-write data from the volatile memory to storage devices when main power is being supplied to the RAID controller prior to the loss thereof, wherein the memory controller buffers the transfers of the posted-write data from the host computers to the volatile memory and the transfers of the posted-write data from the volatile memory to the storage devices when the main power is being supplied to the RAID controller prior to the loss thereof, wherein said CPU is configured to program said source location into said register of said memory controller prior to said loss of main power; and

flushing posted-write data, by the memory controller rather than by the CPU, from the volatile memory to the non-volatile memory, in response to the loss of main power.

144. A method for preserving posted-write data in a write-caching redundant array of inexpensive disks (RAID) controller, the method comprising:

supplying power, by at least one capacitor, to a volatile memory, a non-volatile memory, and a memory controller of the RAID controller, in response to a loss of main power to the RAID controller, wherein said memory controller comprises a first register for specifying a source location of said posted-write data in said volatile memory and a second register for specifying a destination location of said posted-write data in said non-volatile memory, wherein said memory controller flushes said posted-write data from said source location specified in said first register to said destination location specified in said second register;

foregoing supplying power, by the at least one capacitor, to a central processing unit (CPU) of the RAID controller, in response to the loss of main power to the RAID controller, wherein the CPU manages transfers of the posted-write data from host computers to the volatile memory and transfers of the posted-write data from the volatile memory to storage devices when main power is being supplied to the RAID controller prior to the loss thereof, wherein the memory controller buffers the transfers of the posted-write data from the host computers to the volatile memory and the transfers of the posted-write data from the volatile memory to the storage devices when the main power is being supplied to the RAID controller prior to the loss thereof, wherein said CPU is configured to program said destination location into said second register of said memory controller prior to said loss of main power; and

flushing posted-write data, by the memory controller rather than by the CPU, from the volatile memory to the non-volatile memory, in response to the loss of main power.

145. A method for preserving posted-write data in a write-caching redundant array of inexpensive disks (RAID) controller, wherein said posted-write data is comprised in a plurality of non-contiguous regions in a volatile memory, the method comprising:

supplying power, by at least one capacitor, to said volatile memory, a non-volatile memory, and a memory controller of the RAID controller, in response to a loss of main power to the RAID controller;

foregoing supplying power, by the at least one capacitor, to a central processing unit (CPU) of the RAID controller, in response to the loss of main power to the RAID controller, wherein the CPU manages transfers of the posted-write data from host computers to the volatile memory and transfers of the posted-write data from the volatile memory to storage devices when main power is being supplied to the RAID controller prior to the loss thereof, wherein the memory controller buffers the transfers of the posted-write data from the host computers to the volatile memory and the transfers of the posted-write data from the volatile memory to the storage devices when the main power is being supplied to the RAID controller prior to the loss thereof, wherein said CPU is configured to program information specifying said plurality of non-contiguous regions into said memory controller prior to said loss of main power; and

flushing posted-write data, by the memory controller rather than by the CPU, from the volatile memory to the non-volatile memory, in response to the loss of main power.

146. A method for preserving posted-write data in a write-caching redundant array of inexpensive disks (RAID) controller, the method comprising:

supplying power, by at least one capacitor, to a volatile memory, a non-volatile memory, a memory controller, and a power manager of the RAID controller, in response to a loss of main power to the RAID controller, wherein the power manager is coupled to said memory controller, configured to detect said loss of main power, and to signal said memory controller to flush said posted-write data from said volatile memory to said non-volatile memory in response thereto, wherein said memory controller is configured to indicate to said power manager whether said memory controller is presently flushing said posted-write data from said volatile memory to said non-volatile memory, wherein said memory controller is further configured to indicate to said power manager whether an error occurred when said memory controller attempted to flush said posted-write data from said volatile memory to said non-volatile memory;

foregoing supplying power, by the at least one capacitor, to a central processing unit (CPU) of the RAID controller, in response to the loss of main power to the RAID controller, wherein the CPU manages transfers of the posted-write data from host computers to the volatile memory and transfers of the posted-write data from the volatile memory to storage devices when main power is being supplied to the RAID controller prior to the loss thereof, wherein the memory controller buffers the transfers of the posted-write data from the host computers to the volatile memory and the transfers of the posted-write data from the volatile memory to the storage devices when the main power is being supplied to the RAID controller prior to the loss thereof; and

flushing posted-write data, by the memory controller rather than by the CPU, from the volatile memory to the non-volatile memory, in response to the loss of main power.