Partial file restore in a data storage system

Abstract

The data storage system according to certain aspects can implement partial file restore, where only a portion of the secondary copy of a file is restored. Such portion may be designated by one or more application offsets for the file. The system may provide an in-chunk index that includes mapping information between the application offsets and the secondary copy offsets. Chunks may refer to logical data units in which secondary copies are stored, and the in-chunk index for a chunk may be stored in secondary storage with the chunk. Because the mapping information may not be provided at a fixed interval, the system can search through application offsets in the in-chunk index to locate the secondary copy offset corresponding to the portion application offset(s). In this manner, the system may restore the designated portion of the secondary copy in a fast and efficient manner by using the in-chunk index.

What is claimed is: 
     
         1 . A method of storing files in secondary storage in a data storage system, comprising:
 initiating copying of a plurality of files from primary storage to secondary storage, wherein data stored on the secondary storage is organized in one or more chunks, each chunk being a logical data unit;   copying a first portion of a first file of the plurality of files from the primary storage to a buffer for writing to the secondary storage;   creating a first entry in an index associated with a first chunk of the one or more chunks, the index stored in association with the first chunk, the first entry corresponding to the first portion of the first file and comprising:
 a first application offset corresponding to the first portion and associated with a software application used to access the first file; and 
 a first secondary storage offset indicating a location of the first portion within the first chunk in the secondary storage; 
   copying a second portion of the first file from the primary storage to the buffer for writing to the secondary storage;   creating a second entry in the index associated with the first chunk, the second entry comprising:
 a second application offset corresponding to the second portion and associated with the software application; and 
 a second secondary storage offset indicating a location of the second portion within the first chunk in the secondary storage; 
   writing the first portion to the location indicated by the first secondary storage offset; and   writing the second portion to the location indicated by the second secondary storage offset.