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Libero Backup - Redundant backups with alternating incremental parity

IP.com Disclosure Number: IPCOM000125693D
Original Publication Date: 2005-Jun-13
Included in the Prior Art Database: 2005-Jun-13
Document File: 3 page(s) / 70K

Publishing Venue

IBM

Abstract

A backup normally consists of several backup media (mostly tapes). If one medium of the backup gets damaged or lost the complete backup cannot be restored consistently. To solve this issue some companies make mirrored backups for getting two copies of every medium. It is possible to make the backup disaster proof by using two tape libraries in two different location. But that needs two backup libraries and twice the media of a simple backup. A backup solution creating only a few parity media for each backup would be desirable for companies which do not want to afford a mirrored backup. It is possible to create a parity media for each backup instead of mirroring them. This would reduce the number of media of multivolume backups. New is the alternating incremental parity algorithm allowing to secure all incremental backups with only e.g. two parity media. The number of parity media depends only on performance considerations when restoring a failed medium.

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Libero Backup

Libero BackupLibero Backup
Libero Backup

---- Redundant backups with alternating incremental parityRedundant backups with alternating incremental parityRedundant backups with alternating incremental parity

Redundant backups with alternating incremental parity

Why do we need parity?

A backup normally consists of several backup media (mostly tapes). If one medium of the backup gets damaged or lost the complete backup cannot be restored consistently. To solve this issue some companies make mirrored backups for getting two copies of every medium. It is possible to make the backup disaster proof by using two tape libraries in two different location. But that needs two backup libraries and twice the media of a simple backup. A backup solution creating only a few parity media for each backup would be desirable for companies which do not want to afford a mirrored backup.

Figure 1: A Backup with conventional parity

Mirroring and parity is known, so what's new?

    It is possible to create a parity media for each backup instead of mirroring them. This would reduce the number of media of multivolume backups . Single volume backups would have the same amount of media like mirroring . New is the alternating incremental parity algorithm allowing to secure all incremental backups with only e.g. two parity media. The number of parity media depends only on performance considerations when restoring a failed medium . During the backup the new data is "inserted" into the parity stream. The number of parity media does not increase. The incremental parity media have no static position in the backup . They go always to the position where they are needed. Like the "Libero" of a soccer team. Here the source of the naming can be found .

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Figure 2: A Backup with incremental parity

Algorithm

    The incremental parity mediums are created using the former parity information of the parity stream and the new data . In the former example two streams were used: "Medium A" and "Medium B". For the first generation of parity medium of each stream the older sequence is a stream of zero . By inserting the new data into the parity stream the parity is recalculated and the number of parity media can be reduced to the number of desired parity streams . The new parity is calculated with the following algorithm: new parity = former parity XOR backup data [1... n]

Conventional backup: restoring data

The normal way of a conventional backup restoring data is:
1. Read day 1 (full backup...