Extent Mapping Index for Sequential Backup Restore
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Solution Overview
Problem
Existing backup techniques using sequential media are inefficient when restoring individual files from extent-level backups, as they require seeking through large amounts of data to retrieve fragmented file pieces, leading to prolonged restoration times, especially when files are fragmented across significant distances on the backup media.
Innovation Solution
A method that generates and uses a list to identify non-contiguous extents of a storage device, allowing information to be read and written to backup media in a non-contiguous order, reducing fragmentation and enabling faster single-file restores by accessing and writing data in a manner that groups extents storing a file together, thereby reducing the time needed to retrieve the file.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If extent-level backup is performed on sequential media, then backup storage efficiency is improved, but individual file restore time increases significantly
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the mapping between file extents and their locations on sequential backup media during the backup process. This advance preparation creates an extent mapping index that enables rapid file retrieval without requiring sequential scanning of the backup media during restore operations.
Solution Approach 2:
The patent introduces an extent mapping index as an intermediary data structure that bridges the file system and the sequential backup media. This index contains metadata about extent locations and allows the restore process to directly navigate to required file portions without seeking through intervening data on the sequential media.
2Quantity of substance
If files are stored as fragmented extents on storage device, then storage space utilization is improved, but restore performance on sequential media deteriorates
Solution Approach 1:
The extent mapping index serves as an intermediary that decouples the fragmented storage structure from the sequential access medium. It records the logical-to-physical mapping of extents, allowing the system to efficiently locate and retrieve scattered file portions on sequential media without requiring the files to be physically contiguous.
Solution Approach 2:
The system performs preliminary action by pre-recording extent location information during the backup process. This advance mapping allows the restore operation to jump directly to required extents on the sequential media, eliminating the need to sequentially scan through large amounts of intervening data.
3Ease of manufacture
If sequential media is used for backup, then backup simplicity is improved, but random access capability for file restore is lost
Solution Approach 1:
The extent mapping index acts as an intermediary layer that provides random access capability to sequential media. By storing metadata about extent locations, the system can logically access any file portion directly, even though the physical media requires sequential scanning. The index translates logical file offsets into physical media positions.
Solution Approach 2:
The system performs preliminary action by pre-calculating and storing the relationship between file logical addresses and physical media positions during backup. This advance preparation enables rapid navigation to specific file portions during restore operations, effectively providing random access functionality on top of sequential media.
Data Source
AI summary
Various methods and systems for performing extent-level backups that support single file restores are disclosed. For example, one a method involves accessing a list, which identifies several extents of a first storage device in a non-contiguous order. The non-contiguous order is non-contiguous with respect to an order in which the extents are arranged on the first storage device. The method then involves reading information from the extents of the first storage device, in the non-contiguous order identified by the list, and the writing the information to backup media. The information is written to the backup media in the non-contiguous order identified by the list. As a result, a first portion of the information, which is included in a first data object, may be less fragmented on the backup media than on the first storage device.