Content addressable information encapsulation, representation, and transfer

• US 7,475,432 B2
• Filed: 07/19/2004
• Issued: 01/06/2009
• Est. Priority Date: 01/23/1998
• Status: Expired due to Term

• Current Assignee: EMC Corporation (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Van Riel, Jan F., Teugels, Tom, Carpentier, Paul R.
• Primary Examiner(s): Moise; Emmanuel L
• Assistant Examiner(s): CALLAHAN, PAUL E
• Application Number:
  US10/894,284
• Publication Number:
  US 20050010793A1
• Time in Patent Office: 1,632 Days
• Field of Search: 726/4, 726/30, 705/51, 713/165, 369/30.01, 369/27.01, 369/30.03, 711/108, 711/216
• US Class Current: 726/30
• CPC Class Codes: G06F 11/1451 by selection of backup contents
• CPC Class Codes: G06F 11/1453 using de-duplication of the data
• CPC Class Codes: G06F 11/1464 for networked environments
• CPC Class Codes: G06F 16/137 Hash-based content-based indexing of textual data G06F16/31
• CPC Class Codes: H04L 12/1854 with non-centralised forwarding system, e.g. chaincast
• CPC Class Codes: H04L 63/0428 wherein the data content is protected, e.g. by encrypting or encapsulating the payload
• CPC Class Codes: H04L 63/065 for group communications cryptographic mechanisms or cryptographic arrangements for key management involving conference or group key H04L9/0833
• CPC Class Codes: H04L 63/12 Applying verification of the received information cryptographic mechanisms or cryptographic arrangements for data integrity or data verification H04L9/32
• CPC Class Codes: H04L 67/104 Peer-to-peer [P2P] networks
• CPC Class Codes: H04L 67/1068 Discovery involving direct consultation or announcement among potential requesting and potential source peers
• CPC Class Codes: H04L 67/108 characterised by resources being split in blocks or fragments
• CPC Class Codes: H04L 67/56 Provisioning of proxy services store-and-forward switching systems in data switching networks H04L12/54
• CPC Class Codes: H04L 67/566 Grouping or aggregating service requests, e.g. for unified processing
• CPC Class Codes: H04L 67/568 Storing data temporarily at an intermediate stage, e.g. caching

Abstract

Representing a number of assets on an originating computer begins with selecting the assets to be represented. Cryptographic hash asset identifiers are generated; each of the asset identifiers is computed using the contents of a particular asset. The asset identifier is a content-based or content-addressable asset name for the asset and is location independent. An asset list is generated that includes the asset identifiers computed from the assets. A cryptographic hash asset list identifier is generated that is computed from the asset list. The asset list identifier is stored for later retrieval. The assets selected are also stored for safekeeping either locally or on a computer network. In the event of loss of the files from the originating computer, the asset list identifier is retrieved. Using the asset list identifier, the original asset list is found and retrieved from its safe location. The asset identifiers from the retrieved asset list are used to find and retrieve the individual assets from their backup locations. The assets are verified by recomputing the cryptographic hash asset identifier for each asset retrieved and comparing it to the asset identifier from the asset list. The MD5 algorithm is used for the cryptographic hash function. Assets are retrieved using a multicast protocol. A series of importer programs searches for assets to retrieve in progressively more remote locations. Assets are retrieved whole or in segments.

Claims

1. A method for use in a computer system comprising at least first and second computers, wherein the first computer provides content addressable storage, the method comprising acts of:

(A) receiving, at the first computer, a communication from the second computer including a unit of data;

(B) storing the unit of data at a storage location managed by the first computer; and

(C) associating the unit of data with an identifier for the unit of data, wherein the identifier is based, at least in part, on the content of the unit of data and is the only identifier that can be used to identify the unit of data in any communication between the first and second computers.

2. The method of claim 1, wherein the act (C) of associating the unit of data with an identifier comprises an act of associating the storage location at which the unit of data is stored with the identifier.

3. The method of claim 2, wherein the act (C) of associating comprises an act of storing information that associates the storage location with the identifier.

4. The method of claim 2, wherein the act (C) of associating comprises an act of selecting the storage location based, at least in part, on the identifier.

5. The method of claim 1, further comprising an act of receiving the identifier at the first computer.

6. The method of claim 5, wherein the identifier is generated by applying a cryptographic hash function to at least a portion of the content of the unit of data.

7. The method of claim 5, wherein the identifier received at the first computer is a first identifier for the unit of data, and wherein the method further comprises acts of:

(D) generating, at the first computer, a second identifier for the unit of data; and

(E) comparing the second identifier to the first identifier to verify that the first and second identifiers are identical.

8. The method of claim 7, wherein the first identifier is generated by applying a cryptographic hash function to at least a portion of the content of the unit of data, and wherein the act (D) comprises an act of generating the second identifier using the cryptographic hash function on the at least a portion of the content of the unit of data received at the storage system.

9. The method of claim 7, wherein the first identifier is generated by applying a cryptographic hash function to the entire content of the unit of data, and wherein the act (D) comprises an act of generating the second identifier using the cryptographic hash function on the entire content of the unit of data stored received by the first computer.

10. The method of claim 1, further comprising an act, performed by the first computer, of generating the identifier.

11. The method of claim 10, wherein the act of generating the identifier comprises generating the identifier by applying a cryptographic hash function to at least a portion of the content of the unit of data.

12. The method of claim 10, wherein the act of generating the identifier comprises generating the identifier by applying a cryptographic hash function to the entire content of the digital asset.

13. The method of claim 10, further comprising an act of returning the identifier to the second computer that issued the communication.

14. The method of claim 1, wherein the unit of data comprises at least one digital asset.

15. The method of claim 1, wherein the unit of data comprises at least one descriptor file.

16. The method of claim 15, wherein the descriptor file includes a second identifier for at least one digital asset and metadata relating to the at least one digital asset, wherein the second identifier is based, at least in part, on the content of the at least one digital asset.

17. The method of claim 1, wherein the unit of data comprises at least one digital asset and at least one descriptor file.

18. The method of claim 1, wherein the first computer comprises a file system to manage units of data stored by the first computer, wherein the act (B) comprises an act of storing the digital asset in a file in the file system, and wherein the act (C) comprises an act of using the identifier as the name of the file that stores the unit of data.

19. The method of claim 18, wherein the identifier is generated by applying a cryptographic hash function to at least a portion of the content of the unit of data.

20. The method of claim 18, wherein the identifier is generated by applying a cryptographic hash function to the entire content of the unit of data.

21. The method of claim 1, wherein the first computer is a silo.

22. The method of claim 1, wherein the first computer is a file server.

23. The method of claim 1, wherein the first computer is a storage system.

24. The method of claim 1, wherein the computer system comprises a plurality of computers in addition to the first and second computers and wherein the plurality of computers are interconnected by at least one network, and wherein each of the plurality of computers manages storage of one or more units of data.

25. The method of claim 1, wherein the first and second computers are peer computers coupled by at least one network.

26. The method of claim 1, wherein the act (B) comprises storing the unit of data on the first computer.

27. The method of claim 1, wherein the act (B) comprises storing the unit of data on a storage device managed by the first computer.

28. At least one computer readable medium encoded with instructions that, when executed on a computer system, perform a method, wherein the computer system comprises at least first and second computers, wherein the first computer provides content addressable storage, and wherein the method comprises acts of:

(A) receiving a communication from the second computer including a unit of data on the first computer;

(B) storing the unit of data at a storage location managed by the first computer; and

(C) associating the unit of data with an identifier for the unit of data, wherein the identifier is based, at least in part, on the content of the unit of data and is the only identifier that can be used to identify the unit of data in any communication between the first and second computers.

29. The at least one computer readable medium of claim 28, wherein the act (C) of associating the unit of data with an identifier comprises an act of associating the storage location at which the unit of data is stored with the identifier.

30. The at least one computer readable medium of claim 29, wherein the act (C) of associating comprises an act of storing information that associates the storage location with the identifier.

31. The at least one computer readable medium of claim 29, wherein the act (C) of associating comprises an act of selecting the storage location based, at least in part, on the identifier.

32. The at least one computer readable medium of claim 28, wherein the method further comprises an act of receiving the identifier at the first computer.

33. The at least one computer readable medium of claim 32, wherein the identifier is generated by applying a cryptographic hash function to at least a portion of the content of the unit of data.

34. The at least one computer readable medium of claim 32, wherein the identifier received at the first computer is a first identifier for the unit of data, and wherein the method further comprises acts of:

(D) generating, at the first computer, a second identifier for the unit of data; and

(E) comparing the second identifier to the first identifier to verify that the first and second identifiers are identical.

35. The at least one computer readable medium of claim 34, wherein the first identifier is generated by applying a cryptographic hash function to at least a portion of the content of the unit of data, and wherein the act (D) comprises an act of generating the second identifier using the cryptographic hash function on the at least a portion of the content of the unit of data received at the storage system.

36. The at least one computer readable medium of claim 34, wherein the first identifier is generated by applying a cryptographic hash function to the entire content of the unit of data, and wherein the act (D) comprises an act of generating the second identifier using the cryptographic hash function on the entire content of the unit of data stored received by the first computer.

37. The at least one computer readable medium of claim 28, wherein the method further comprises an act, performed by the first computer, of generating the identifier.

38. The at least one computer readable medium of claim 37, wherein the act of generating the identifier comprises generating the identifier by applying a cryptographic hash function to at least a portion of the content of the unit of data.

39. The at least one computer readable medium of claim 37, wherein the act of generating the identifier comprises generating the identifier by applying a cryptographic hash function to the entire content of the digital asset.

40. The at least one computer readable medium of claim 37, wherein the method further comprises an act of returning the identifier to the second computer that issued the communication.

41. The at least one computer readable medium of claim 28, wherein the method further comprises at least one digital asset.

42. The at least one computer readable medium of claim 28, wherein the unit of data comprises at least one descriptor file.

43. The at least one computer readable medium of claim 42, wherein the descriptor file includes a second identifier for at least one digital asset and metadata relating to the at least one digital asset, wherein the second identifier is based, at least in part, on the content of the at least one digital asset.

44. The at least one computer readable medium of claim 28, wherein the unit of data comprises at least one digital asset and at least one descriptor file.

45. The at least one computer readable medium of claim 28, wherein the first computer comprises a file system to manage units of data stored by the first computer, wherein the act (B) comprises an act of storing the digital asset in a file in the file system, and wherein the act (C) comprises an act of using the identifier as the name of the file that stores the unit of data.

46. The at least one computer readable medium of claim 45, wherein the identifier is generated by applying a cryptographic hash function to at least a portion of the content of the unit of data.

47. The at least one computer readable medium of claim 45, wherein the identifier is generated by applying a cryptographic hash function to the entire content of the unit of data.

48. The at least one computer readable medium of claim 28, wherein the first computer is a silo.

49. The at least one computer readable medium of claim 28, wherein the first computer is a file server.

50. The at least one computer readable medium of claim 28, wherein the first computer is a storage system.

51. The at least one computer readable medium of claim 28, wherein the computer system comprises a plurality of computers in addition to the first and second computers and wherein the plurality of computers are interconnected by at least one network, and wherein each of the plurality of computers manages storage of one or more units of data.

52. The at least one computer readable medium of claim 28, wherein the first and second computers are peer computers coupled by at least one network.

53. The at least one computer readable medium of claim 28, wherein the act (B) comprises storing the unit of data on the first computer.

54. The at least one computer readable medium of claim 28, wherein the act (B) comprises storing the unit of data on a storage device managed by the first computer.

55. A first computer that provides content addressable storage for use in a computer system comprising the first computer and a second computer, the first computer comprising:

at least one storage device; and

at least one controller, coupled to the at least one storage device, that;

provides a communication interface for communication between the first and second computers, wherein an identifier for a unit of data, which is based, at least in part, on the unit of data, is the only identifier that can be used to identify the unit of data via the communication interface;

receives a communication from the second computer via the communication interface including the unit of data on the first computer; and

stores the unit of data at a storage location on the at least one storage device.

56. The first computer of claim 55, wherein the at least one controller associates the storage location at which the unit of data is stored with the identifier.

57. The first computer of claim 56, wherein the at least one controller stores information that associates the storage location with the identifier.

58. The first computer of claim 56, wherein the at least one controller selects the storage location based, at least in part, on the identifier.

59. The first computer of claim 55, wherein the at least one controller receives the identifier.

60. The first computer of claim 59, wherein the identifier is generated by applying a cryptographic hash function to at least a portion of the content of the unit of data.

61. The first computer of claim 59, wherein the identifier received at the first computer is a first identifier for the unit of data, and wherein the at least one controller:

generates a second identifier for the unit of data; and

compares the second identifier to the first identifier to verify that the first and second identifiers are identical.

62. The first computer of claim 61, wherein the first identifier is generated by applying a cryptographic hash function to at least a portion of the content of the unit of data, and wherein the at least one controller generates the second identifier using the cryptographic hash function on the at least a portion of the content of the unit of data received at the storage system.

63. The first computer of claim 61, wherein the first identifier is generated by applying a cryptographic hash function to the entire content of the unit of data, and wherein the at least one controller generates the second identifier using the cryptographic hash function on the entire content of the unit of data stored received by the first computer.

64. The first computer of claim 55, wherein the at least one controller generates the identifier.

65. The first computer of claim 64, wherein the at least one controller generates the identifier by applying a cryptographic hash function to at least a portion of the content of the unit of data.

66. The first computer of claim 64, wherein the at least one controller generates the identifier by applying a cryptographic hash function to the entire content of the digital asset.

67. The first computer of claim 64, wherein the at least one controller returns the identifier to the second computer that issued the communication.

68. The first computer of claim 55, wherein the unit of data comprises at least one digital asset.

69. The first computer of claim 55, wherein the unit of data comprises at least one descriptor file.

70. The first computer of claim 69, wherein the descriptor file includes a second identifier for at least one digital asset and metadata relating to the at least one digital asset, wherein the second identifier is based, at least in part, on the content of the at least one digital asset.

71. The first computer of claim 55, wherein the unit of data comprises at least one digital asset and at least one descriptor file.

72. The first computer of claim 55, wherein the first computer comprises a file system to manage units of data stored by the first computer, wherein the at least one controller stores the digital asset in a file in the file system and uses the identifier as the name of the file that stores the unit of data.

73. The first computer of claim 72, wherein the identifier is generated by applying a cryptographic hash function to at least a portion of the content of the unit of data.

74. The first computer of claim 72, wherein the identifier is generated by applying a cryptographic hash function to the entire content of the unit of data.

75. The first computer of claim 55, wherein the first computer is a silo.

76. The first computer of claim 55, wherein the first computer is a file server.

77. The first computer of claim 55, wherein the first computer is a storage system.

78. The first computer of claim 55, wherein the computer system comprises a plurality of computers in addition to the first and second computers and wherein the plurality of computers are interconnected by at least one network, and wherein each of the plurality of computers manages storage of one or more units of data.

79. The first computer of claim 55, wherein the first and second computers are peer computers coupled by at least one network.

80. The first computer of claim 55, wherein the at least one controller stores the unit of data on the first computer.

81. The first computer of claim 55, wherein the at least one controller stores the unit of data on a storage device managed by the first computer.

82. A method for use in a computer system comprising at least first and second computers, wherein the first computer provides content addressable storage, the method comprising acts of:

(A) transmitting, from the second computer, a communication to the first computer including a unit of data; and

(B) associating, at the second computer, the unit of data with an identifier for the unit of data, wherein the identifier is based, at least in part, on the content of the unit of data and is the only identifier that can be used to identify the unit of data in any communication between the first and second computers.

83. The method of claim 82, wherein the act (B) of associating comprises an act of storing information that associates the unit of data with the identifier.

84. The method of claim 82, wherein the identifier is generated by the first computer, and wherein the method further comprises an act of receiving the identifier at the second computer.

85. The method of claim 84, wherein the act of receiving the identifier comprises an act of receiving an identifier generated by applying a cryptographic hash function to at least a portion of the content of the unit of data.

86. The method of claim 82, further comprising an act, performed by the second computer, of generating the identifier.

87. The method of claim 86, further comprising an act of transmitting the identifier to the first computer.

88. The method of claim 87, wherein the identifier generated by the second computer is a first identifier for the unit of data, and wherein the method further comprises acts of:

(C) transmitting the unit of data from the second computer to the first computer;

(D) receiving, at the second computer, a second identifier for the unit of data generated by the first computer; and

(E) comparing the second identifier to the first identifier to verify that the first and second identifiers are identical.

89. The method of claim 88, wherein the act, performed by the second computer, of generating the first identifier comprises an act of generating the first identifier by applying a cryptographic hash function to at least a portion of the content of the unit of data.

90. The method of claim 88, wherein the act, performed by the second computer, of generating the first identifier comprises an act of generating the first identifier by applying a cryptographic hash function to the entire content of the unit of data.

91. The method of claim 86, further comprising an act of transmitting the identifier to the first computer along with the communication.

92. The method of claim 86, wherein the act of generating the identifier comprises generating the identifier by applying a cryptographic hash function to at least a portion of the content of the unit of data.

93. The method of claim 86, wherein the act of generating the identifier comprises generating the identifier by applying a cryptographic hash function to the entire content of the unit of data.

94. The method of claim 82, wherein the unit of data comprises at least one digital asset.

95. The method of claim 82, wherein the unit of data comprises a content descriptor file.

96. The method of claim 95, wherein the descriptor file includes a second identifier for at least one digital asset and metadata relating to the at least one digital asset, wherein the second identifier is based, at least in part, on the content of the at least one digital asset.

97. The method of claim 82, wherein the unit of data comprises at least one digital asset and at least one content descriptor file.

98. The method of claim 82, wherein the first computer is a silo.

99. The method of claim 82, wherein the act (A) comprises an act of transmitting the unit of data from the second computer to the first computer along with the communication.

100. The method of claim 99, wherein the act (A) comprises an act of transmitting the unit of data in the communication.

101. The method of claim 82, further comprising an act of transmitting, from the second computer to the first computer, a request to read the unit of data stored by the first computer, the request identifying the unit of data via the identifier.

102. The method of claim 82, wherein the first computer is a file server.

103. The method of claim 82, wherein the first computer is a storage system.

104. The method of claim 82, wherein the computer system comprises a plurality of computers in addition to the first and second computers, wherein the plurality of computers are interconnected by at least one network, and wherein each of the plurality of computers manages storage of one or more unit of data.

105. The method of claim 82, wherein the first and second computers are peer computers coupled by at least one network.

106. At least one computer readable medium encoded with instructions that, when executed on a computer system perform a method, wherein the computer system comprises at least first and second computers, wherein the first computer provides content addressable storage, and wherein the method comprises acts of:

(A) transmitting, from the second computer, a communication to the first computer including a unit of data; and

(B) associating, at the second computer, the unit of data with an identifier for the unit of data, wherein the identifier is based, at least in part, on the content of the unit of data and is the only identifier that can be used to identify the unit of data in any communication between the first and second computers.

107. The at least one computer readable medium of claim 106, wherein the act (B) of associating comprises an act of storing information that associates the unit of data with the identifier.

108. The at least one computer readable medium of claim 106, wherein the identifier is generated by the first computer, and wherein the method further comprises an act of receiving the identifier at the second computer.

109. The at least one computer readable medium of claim 108, wherein the act of receiving the identifier comprises an act of receiving an identifier generated by applying a cryptographic hash function to at least a portion of the content of the unit of data.

110. The at least one computer readable medium of claim 106, wherein the method further comprises an act of generating the identifier.

111. The at least one computer readable medium of claim 110, wherein the method further comprises an act of transmitting the identifier to the first computer.

112. The at least one computer readable medium of claim 111, wherein the identifier is a first identifier for the unit of data, and wherein the method further comprises acts of:

(C) transmitting the unit of data from the second computer to the first computer;

(D) receiving, at the second computer, a second identifier for the unit of data generated by the first computer; and

(E) comparing the second identifier to the first identifier to verify that the first and second identifiers are identical.

113. The at least one computer readable medium of claim 112, wherein the act of generating the first identifier comprises an act of generating the first identifier by applying a cryptographic hash function to at least a portion of the content of the unit of data.

114. The at least one computer readable medium of claim 112, wherein the act of generating the first identifier comprises an act of generating the first identifier by applying a cryptographic hash function to the entire content of the unit of data.

115. The at least one computer readable medium of claim 110, wherein the method further comprises an act of transmitting the identifier to the first computer along with the communication.

116. The at least one computer readable medium of claim 110, wherein the act of generating the identifier comprises generating the identifier by applying a cryptographic hash function to at least a portion of the content of the unit of data.

117. The at least one computer readable medium of claim 110, wherein the act of generating the identifier comprises generating the identifier by applying a cryptographic hash function to the entire content of the unit of data.

118. The at least one computer readable medium of claim 106, wherein the unit of data comprises at least one digital asset.

119. The at least one computer readable medium of claim 106, wherein the unit of data comprises a content descriptor file.

120. The at least one computer readable medium of claim 119, wherein the descriptor file includes a second identifier for at least one digital asset and metadata relating to the at least one digital asset, wherein the second identifier is based, at least in part, on the content of the at least one digital asset.

121. The at least one computer readable medium of claim 106, wherein the unit of data comprises at least one digital asset and at least one content descriptor file.

122. The at least one computer readable medium of claim 106, wherein the first computer is a silo.

123. The at least one computer readable medium of claim 106, wherein the act (A) comprises an act of transmitting the unit of data from the second computer to the first computer along with the communication.

124. The at least one computer readable medium of claim 123, wherein the act (A) comprises an act of transmitting the unit of data in the communication.

125. The at least one computer readable medium of claim 106, further comprising an act of transmitting, from the second computer to the first computer, a request to read the unit of data stored by the first computer, the request identifying the unit of data via the identifier.

126. The at least one computer readable medium of claim 106, wherein the first computer is a file server.

127. The at least one computer readable medium of claim 106, wherein the first computer is a storage system.

128. The at least one computer readable medium of claim 106, wherein the computer system comprises a plurality of computers in addition to the first and second computers, wherein the plurality of computers are interconnected by at least one network, and wherein each of the plurality of computers manages storage of one or more unit of data.

129. The at least one computer readable medium of claim 106, wherein the first and second computers are peer computers coupled by at least one network.

130. A first computer for use in a computer system comprising the first computer and a second computer, wherein the second computer provides content addressable storage, and wherein the first computer comprises:

an output for transmitting access requests; and

at least one controller, coupled to the output, that;

provides a communication interface for communication between the first and second computers, wherein an identifier for a unit of data, which is based, at least in part, on the unit of data, is the only identifier that can be used to identify the unit of data via the communication interface; and

transmits a communication to the second computer via the communication interface including the unit of data.

131. The first computer of claim 130, wherein the at least one controller stores information that associates the unit of data with the identifier.

132. The first computer of claim 130, wherein the identifier is generated by the second computer, and wherein the at least one controller receives the identifier.

133. The first computer of claim 132, wherein the at least one controller receives an identifier generated by applying a cryptographic hash function to at least a portion of the content of the unit of data.

134. The first computer of claim 130, wherein the at least one controller generates the identifier.

135. The first computer of claim 134, wherein the at least one controller transmits the identifier to the second computer along with the communication.

136. The first computer of claim 134, wherein the at least one controller generates the identifier by applying a cryptographic hash function to at least a portion of the content of the unit of data.

137. The first computer of claim 134, wherein the at least one controller transmits the identifier to the second computer.

138. The first computer of claim 137, wherein the identifier generated by the first computer is a first identifier for the unit of data, and wherein the at least one controller:

transmits the unit of data to the second computer;

receives a second identifier for the unit of data generated by the second computer; and

compares the second identifier to the first identifier to verify that the first and second identifiers are identical.

139. The first computer of claim 138, wherein the at least one controller generates the first identifier by applying a cryptographic hash function to at least a portion of the content of the unit of data.

140. The first computer of claim 138, wherein the at least one controller generates the first identifier by applying a cryptographic hash function to the entire content of the unit of data.

141. The first computer of claim 134, wherein the at least one controller generates the identifier by applying a cryptographic hash function to the entire content of the unit of data.

142. The first computer of claim 130, wherein the unit of data comprises at least one digital asset.

143. The first computer of claim 130, wherein the unit of data comprises a content descriptor file.

144. The first computer of claim 143, wherein the descriptor file includes a second identifier for at least one digital asset and metadata relating to the at least one digital asset, wherein the second identifier is based, at least in part, on the content of the at least one digital asset.

145. The first computer of claim 130, wherein the unit of data comprises at least one digital asset and at least one content descriptor file.

146. The first computer of claim 130, wherein the second computer is a silo.

147. The first computer of claim 130, wherein the at least one controller transmits the unit of data to the second computer along with the communication.

148. The first computer of claim 130, wherein the at least one controller transmits the unit of data in the communication.

149. The first computer of claim 130, wherein the at least one controller transmits, to the second computer, a request to read the unit of data stored by the second computer, the request identifying the unit of data via the identifier.

150. The first computer of claim 130, wherein the second computer is a file server.

151. The first computer of claim 130, wherein the second computer is a storage system.

152. The first computer of claim 130, wherein the computer system comprises a plurality of computers in addition to the first and first computers, wherein the plurality of computers are interconnected by at least one network, and wherein each of the plurality of computers manages storage of one or more unit of data.

153. The first computer of claim 130, wherein the first and first computers are peer computers coupled by at least one network.