Defining a Safe Rotation Scheme for Business Continuity
Our clients often ask us for guidance when it comes to backing up their data on tapes. How often? What is required for our employees? One of the key elements of any backup plan is…
The best rotation schedule is one that provides you with a long, deep and varied history of file versions. This contrasts with a tape-a-day scheme, for instance, that merely overwrites data from the day previous. Let’s explore the foundations to a secure rotation scheme.
Protecting your data at least once per day is essential. However, the cost or time required to do a full back up every day can be impractical, especially for companies with vast amounts of data. Many users, therefore, will do an incremental or differential back up on most days. Differential backups back up every file that has changed since the last full backup. Incremental backups back up only files that have changed since the previous incremental or full backup. Finding a specific file to restore is more difficult with these partial backups since it may be on one of several tapes.
At least once per week, a full back up should be performed. This will provide a recent record of all files, minimising the number of tapes to search for a recent copy of a single file. Full backups also create a level of redundancy for most files, duplicating exactly any files that have changed during the week as well as duplicating any files that exist on the prior week’s full backup.
Here, we outline two popular rotation schemes that are offered as configurable backup patterns by most backup application software. Both offer a great depth of file versions. You can choose the one that works for you, or customise one to your own needs. Then, make sure to put it in place at all locations and across all types of data on every platform.
The most commonly used media rotation schedule is ‘Grandfather-Father-Son.’ This scheme uses daily (Son), weekly (Father) and monthly (Grandfather) backup sets.
This scheme begins with the daily back ups. Typically, four backup media are labelled for the day of the week each backs up. For example, Monday through Thursday. Each tape is recalled for use on its labelled day. If only a one-week version history of files is maintained, then each tape is overwritten weekly. To maintain a three-week version history of files (recommended), more tapes are required. For example, this week’s Monday tape will not be overwritten for three weeks. For more information, please see When is it Safe to Overwrite.
Weekly back ups follow a similar scenario. A set of up to five weekly backup media is labelled ‘Week1’, ‘Week2’ and so on. Full back ups are recorded weekly, on the day that a ‘Son’ media is not used. Following the example above these would be ‘Friday’ tapes. This ‘Father’ media is re-used monthly.
Five weekly tapes are required in order to maintain a one-month history of files, as some months have five weeks.
Completing the Pattern
The final set of three media is labelled ‘Month1’, ‘Month2’ and so on, according to which month of the quarter they will be used. This ‘Grandfather’ media records full back ups on the last business day of each month.
If your back up plan follows a corporate fiscal calendar, then your monthly tape will take the place of the Week4 or Week5 weekly/Father tape, depending on the month.
If your back up schedule follows calendar months, then your monthly back up will vary throughout the year, replacing a daily or weekly tape. Typically, monthly tapes are overwritten quarterly or yearly (recommended), depending on version history requirements.
Each of these ‘media’ may be a single tape or a set of tapes, depending on the amount of data to back up and the type of back up used (incremental vs. full). Weekly and/or monthly tapes are generally considered as archive tapes.
For any queries on this rotation scheme, please contact our experts today.
Tower of Hanoi
The second most common rotation scheme, Tower of Hanoi, is based on the mathematical game that bears the same name. In this schedule, one media set “A” is used every other back up session (daily sessions in this example).
- Start Day 1 with ‘A’ and repeat every other back up (every other day).
- The next media set ‘B’ starts on the first non- ‘A’ back up day and repeats every fourth back up session.
- Media set ‘C’ starts on the first non- ‘A’ or non- ‘B’ back up day and repeats every eighth session.
- Media set ‘D’ starts on the first non- ‘A’, ‘B’, or ‘C’ back up day and repeats every sixteenth session.
- Media set ‘E’ alternates with media set ‘D’.
The advantage to the Tower of Hanoi scheme is that with each new media set added to the rotation, the backup history doubles. The frequently used media sets have the most recent copies of a file, whereas less frequently used media retain older versions.
This back up scheme can be difficult to keep track of manually and therefore is generally done with the help of rotation schemes provided in back up software packages.
As with the Grandfather-Father-Son rotation scheme, tapes should be periodically removed from the rotation for archive purposes.
Long-Term Data Storage: Archiving
Archiving for additional data protection is arguably more important than saving tax records. You need long-term archived media in addition to routine backups.
As discussed, archive tapes are generated weekly, monthly, or quarterly. However, an additional yearly archive tape is essential. A set of archive tapes is usually generated to coincide with month-end, quarter-end and year-end financial activities.
An absolute must for archive/long-term data storage tapes is to create a duplicate data set on separate media. Due to the academic, historical, financial or legal (especially the legal) reasons for which data is archived, you cannot risk the vulnerability of one set alone. Mishandling, natural disaster, inappropriate environmental conditions or misplacement of a single copy of your archive data could put you or your company in legal jeopardy. Furthermore, keep in mind that multiple copies of the same data set should not be stored in the same geographic location. See here for more information on off-site storage.
Our backup media specialists are a wealth of knowledge on this topic and happy to help determine which back up rotation scheme is most suited to your unique concerns. Please contact our team today for more information.