Multi-tier file system with transparent holes

A device that provides access to content in a multi-tier file system, the device including:

• a processor, memory coupled to the processor, and computer instructions loaded into the memory that, when executed, cause the processor to implement a process that includes:
• using a file system having a first tier file in persistent memory, and the file system running on a hardware processor:
• the file system automatically initializing a second tier file in the persistent memory, wherein the second tier file is accessible using a same path and file name as the first tier file, and the second tier file has one or more holes as placeholders for data in the first tier file, the holes having links that refer read access to blocks in one or more earlier tiers of the second tier file;
• copying forward blocks of data from the first tier file to the second tier file, at an earlier of as scheduled or responsive to an authorized write access to a particular block of the second tier file;
• and
• prior to completion of the copying forward, the file system responding to an access request by accessing the second tier file by providing data available from the second tier file that has been copied forward and by following links associated with the holes to access blocks in the first tier file to provide data from the first tier file.

A tangible computer readable storage medium that stores program instructions that, when executed, cause a computer to implement a method of access to content in a multi-tier file system, the implementation including:

• using a file system having a first tier file in persistent memory, and the file system running on a hardware processor:
• the file system automatically initializing a second tier file in the persistent memory, wherein the second tier file is accessible using a same path and file name as the first tier file, and the second tier file has one or more holes as placeholders for data in the first tier file, the holes having links that refer read access to blocks in one or more earlier tiers of the second tier file;
• copying forward blocks of data from the first tier file to the second tier file, at an earlier of as scheduled or responsive to an authorized write access to a particular block of the second tier file;
• and
• prior to completion of the copying forward, the file system responding to an access request by accessing the second tier file by providing data available from the second tier file that has been copied forward and by following links associated with the holes to access blocks in the first tier file to provide data from the first tier file.