Using data copies for redundancy

Details Using data copies for redundancy Using data copies for redundancy

2007-09-28

2009-06-16

Sough, Hyung S (Department: 2188)

Electrical computers and digital processing systems: memory

Storage accessing and control

Control technique

C711S114000, C711S154000, C709S216000

Reexamination Certificate

active

07549032

ABSTRACT:
An apparatus and method implemented by a computer system of using data copies of a volume for redundancy when data of the volume is rendered corrupted or inaccessible. In one embodiment of the method a data volume is created. The data volume comprises a plurality of data blocks including a first data block. After creation of the data volume, a point-in-time (PIT) copy or a replica copy of the data volume is created, and a redirection map is created. The redirection map comprises a plurality of entries, wherein each entry of the map indicates whether memories allocated to store data of respective data blocks of the data volume and the PIT copy or the replica copy, contain identical data. Data of the data volume may become corrupt or inaccessible after creation of the PIT copy or replica copy. For example, suppose an I/O transaction is generated to read data from or write data to memory allocated to store data of the first data block of the data volume, and it is discovered that the memory allocated to store data of the first data block is inaccessible as a result of physical damage to this memory. The redirection map and the PIT copy or replica copy can be used to overcome inaccessibility of memory allocated to the first block. If an entry in the redirection map indicates that identical data is stored in memories allocated to the first data block of the data volume and the first data block of the PIT copy (or replica copy), respectively, data is read from memory allocated to store data of a first block of the PIT copy or the replica copy, and possibly stored in new memory allocated to store data of the first data block of the data volume.

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