Donald G Logan

US Patent:

51465710, Sep 8, 1992

Filed:

Feb 26, 1990

Appl. No.:

7/488454

Inventors:

Donald G. Logan - Blackstone MA

Assignee:

EMC Corporation - Hopkington MA

International Classification:

G06F 1122

US Classification:

395400

Abstract:

A method and apparatus are disclosed for mapping a logical address generated by a device seeking access to a storage media into a corresponding physical address to create the appearance that all good addresses consitute a continuous defect free address space in the storage medium. A tree structure is created based upon known defective addresses in the storage medium. The upper levels of the tree are selectively loaded with decisional criteria which are employed to branch downward to an offset value stored in the lowest tree level. The respective offset value is added to the logical address to produce the desired physical address of the storage media for access. The tree is traversed each time an address is presented to map the requested logical address into a physical address corresponding to a location in the storage device for access. The media thus appears to the requesting device to be a continuous defect free address space with defective addresses congregated at the end of the address space, thereby avoiding the need for the requesting device to fragment files due to media defects.