Files having unallocated portions within content addressable storage

A system for generating a content addressable storage (CAS) signature for a file having allocated and unallocated blocks, the system comprising:

• a client device configured with a client interface module, a non-transitory computer readable storage medium, and a processor that is configured to:
• generate a first level of CAS signatures by:
• applying a hash function to allocated blocks of the file to generate CAS signatures, and
• applying a common CAS signature, wherein the common CAS signature represents one or more unallocated blocks, to each unallocated block;
• encoding the first level of CAS signatures with a hash tree depth for the first level of CAS signatures, a block size and a file size;
• and
• generate a second level of one or more CAS signatures by:
• combining the first level of CAS signatures into groups,
• applying a hash function to groups of combined CAS signatures that are derived from at least one allocated block,
• applying the common CAS signature to at least one group with unallocated blocks,
• encoding the second level of CAS signatures with a hash tree depth for the second level of CAS signatures, the block size and the file size;
• and
• store the first level of CAS signatures and the second level of one or more CAS signatures in the non-transitory computer readable storage medium;
• wherein the processor is configured to, responsive to a request from the client interface module to restore the file, output a set of blocks corresponding to the file;
• and
• wherein the set of blocks does not contain any block encoded with the common CAS signature.

A computer program product for loading a file from a content addressable storage (CAS) system having allocated and unallocated blocks, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to:

• retrieve, responsive to a request for the file, first tree data from a first node in a hash tree that represents the file, the first tree data including a first hash tree depth, a first CAS signature, a block size and a file size;
• retrieve respective tree data from respective higher nodes of the hash tree that represents the file, the respective tree data including respective CAS signatures;
• determine that at least one respective CAS signature corresponding to a respective node matches a reserved CAS signature, wherein the reserved CAS signature represents one or more unallocated blocks;
• and
• output, in response to retrieving respective tree data, a set of blocks corresponding to a set of nodes in the hash tree that represents the file, wherein the set of blocks does not include respective blocks corresponding to respective nodes having a CAS signature matching the reserved CAS signature.

A computer program product for generating a content addressable storage (CAS) signature for a file having allocated and unallocated blocks, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to:

• generate a first level of CAS signatures by:
• applying a hash function to allocated blocks of the file to generate CAS signatures, and
• applying a common CAS signature, wherein the common CAS signature represents one or more unallocated blocks, to each unallocated block;
• encoding the first level of CAS signatures with a hash tree depth for the first level of CAS signatures, a block size and a file size;
• and
• generate a second level of one or more CAS signatures by:
• combining the first level of CAS signatures into groups,
• applying a hash function to groups of combined CAS signatures that are derived from at least one allocated block,
• applying the common CAS signature to at least one group with unallocated blocks,
• encoding the second level of CAS signatures with a hash tree depth for the second level of CAS signatures, the block size and the file size;
• and
• store the first level of CAS signatures and the second level of one or more CAS signatures;
• wherein the program instructions are configured to cause the processor to, responsive to a request, output a set of blocks corresponding to the file;
• and
• wherein the set of blocks does not contain any block encoded with the common CAS signature.