Backup rotation scheme

Backup rotation scheme

A backup rotation scheme is a method for effectively backing up data where multiple media (such as tapes) are used in the backup process. The scheme determines how and when each piece of removable storage is used for a backup job and how long it is retained once it has backup data stored on it. Different techniques have evolved over time to balance data retention and restoration needs with the cost of extra data storage media. Such a scheme can be quite complicated if it takes incremental backups, multiple retention periods, and off-site storage into consideration.

Schemes

Incremental backup

*Used to keep the longest possible tail of daily backups
*Archived backups not as important (ie no need to go back 1 year)
*Useful when data before the rotation period is irrelevant

Basically, the incremental backup is just backing up onto the oldest media in the set.So with a daily backup onto a set of 14 media, you would have 14 days worth of individual daily backups, when all the tapes are used, the oldest one is inserted.

This is the simple method that first comes to mind to most new computer users wanting to do backups. It was commonly used when people backed up regularly to floppy disks.

Grandfather, Father, Son

*Enables certain backups to be kept much longer.
*Have more copies available of recent backups, and progressively less as you need to go back over time.

This is one of the most popular method as it achieves multiple aims in having multiple recent backups as well as the ability to refer to past revisions as well as archived data.

Towers of Hanoi

The Towers of Hanoi rotation method is more complex. It is based on the mathematics of the Tower of Hanoi puzzle, with what is essentially a recursive method. It is a 'smart' way of archiving an effective number of backups as well as the ability to go back over time, but it is more complex to understand. Basically, every tape is associated with a disk in the puzzle, and every disk movement to a different peg corresponds with a backup to that tape. So the first tape is used every other day (1, 3, 5, 7, 9,...), the second tape is used every fourth day (2, 6, 10, ...), the third tape is used every eighth day (4, 12, 20, ...). [cite web | url = http://www.computer-repair.com/Backup.htm | title = Backup Methods | author = San Francisco Computer Repair | date = 2008-01-13 | accessdate = 2008-02-21 ]

A set of "n" tapes (or tapes sets) will allow backups for "2 n - 1" days before the last set is recycled. So, three tapes will give four days worth of backups and on the fifth day "Set C" will be overwritten; four tapes will give eight days, and "Set D" is overwritten on the ninth day; five tapes will give 16 days, "etc". Files can be restored from 1, 2, 4, 8, 16, ..., "2 n - 1" days ago. [cite web | url = http://www.alvechurchdata.co.uk/softhanoi.htm | title = Tower of Hanoi pattern for backup | author = Alvechurch Data Ltd | accessdate= 2008-03-12 | date = 2007-11-27]

Mathematically, you can look at the sequence of the binary notation of an incrementing "n"-bit number (starting from zero). In each step, the position of the rightmost zero determines the tape number to use.

The following tables show which tapes are used on which days of various cycles.

Three-Tape Hanoi Schedule

Incremented media method

This method has many variations and names. A set of numbered media is used until the end of the cycle. Then the cycle is repeated using media numbered the same as the previous cycle, but incremented by one. The lowest numbered tape from the previous cycle is retired and kept permanently. Thus, one has access to every backup for one cycle, and one backup per cycle before that. This method has the advantage of ensuring even media wear, but requires a schedule to be precalculated. The system is generally too complex to mentally calculate the next media to be used.

See also

* Backup
* Off-site Data Protection

References


Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Backup — For other uses of Backup , see Backup (disambiguation). In information technology, a backup or the process of backing up is making copies of data which may be used to restore the original after a data loss event. The verb form is back up in two… …   Wikipedia

  • Grandfather-father-son backup — refers to the most common rotation scheme for rotating backup media. Originally designed for tape back up, it works well for any hierarchical backup strategy. The basic method is to define three sets of backups, such as daily, weekly and monthly …   Wikipedia

  • Incremental backup — An incremental backup preserves data by not creating multiple copies that are based on the differences in those data: a successive copy of the data contains only that portion which has changed since the preceding copy has been created. Contents 1 …   Wikipedia

  • Grandfather-Father-Son Backup — (en français « grand père père fils »), est une méthode de rotation de sauvegarde de données utilisée assez couramment. Utilisée à l origine pour les sauvegardes sur bande magnétique, elle fonctionne pour n importe quelle sauvegarde… …   Wikipédia en Français

  • Glossary of backup terms — This page is a glossary of backup terms.*backup policy an organisation s procedures and rules for ensuring that adequate amounts and types of backups are made, including suitably frequent testing of the process for restoring the original… …   Wikipedia

  • Tower of Hanoi — The Tower of Hanoi or Towers of Hanoi (also known as The Towers of Bramha) is a mathematical game or puzzle. It consists of three rods, and a number of disks of different sizes which can slide onto any rod. The puzzle starts with the disks neatly …   Wikipedia

  • Neil Armstrong — For other uses, see Neil Armstrong (disambiguation) …   Wikipedia

  • Hard disk drive — Hard drive redirects here. For other uses, see Hard drive (disambiguation). Hard disk drive Mechanical interior of a modern hard disk drive Date invented 24 December 1954 [1] …   Wikipedia

  • Wikipedia:Reference desk/Computing — The Wikipedia Reference Desk covering the topic of computing. Computing #eee #f5f5f5 #eee #aaa #aaa #aaa #00f #36b #000 #00f computing Wikipedia:Reference de …   Wikipedia

  • RAID — This article is about the data storage technology. For other uses, see Raid (disambiguation). RAID, an acronym for Redundant Array of Independent Disks (originally Redundant Array of Inexpensive Disks),[1] is a storage… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”