| 摘要 |
A backup system enables unmodified data to be copied to a read-only backup container that is smaller than the read-write container. The system creates and maintains structures that map the unmodified copies of data in the backing store container to locations in the read-write container. The mapping structures contain addresses of locations in the backing store container where collections of blocks of data are stored based on the original data block address of the data in the read-write container. In order to obtain the address of the location in the backing store container where a block of data is stored, the system converts the physical block number of the read-write block of data into a physical block address in the backing store container which actually contains the data. By using these mapping structures, the system provides an efficient manner of utilizing a smaller backing store container or less storage space, since the data modified during the snapshot backup process is usually substantially less than read-write on-line data.
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