Basic backup question.

zzpack · 26 Mar 2013

I´m pretty new to backup in general.

In theory, what will happen in the following scenario? If using the grandfather-father-son strategy,
i.e monthly-weekly-daily.

One weekly backup job has failed. The next day and the following working days, the daily backup runs fine. Then, the next weekend the weekly job runs fine.

Will I simply loose one whole week backup, when the monthly backup job is run at the end of the month?
(I know, I can re-run the weekly job, but I´m curious to the answer anyway).

Barman58 · 26 Mar 2013

The Grandfather - Father - Son strategy is more related to the number of backups you retain rather than the frequency of backups, The Grandfather - Father - Son refers to copies, (or more precisely off line media, containing the backups) of the last three backups. This stratagy allows you to go back up to three data-sets for any backup you run. In your example this would mean you could go back to a state as it was, up to, three days ago, Three Weeks ago, or Three Months ago. it comes from the use of tape backups where three tapes were used for backups and the oldest tape in the set was used for the current backup

The result of your failure scenario would depend on the nature of your backups

if the daily backups are incrementally linked to your weekly backup, ie. they backup changes from the last weekly backup then you could loose the first days changes (when the weekly was run but not the daily ), if the Daily backups are run every day, and re-set weekly, you should be able to reconstruct all data as long as each daily backup includes all changes from the reset point, rather than just the daily changes.

zzpack · 26 Mar 2013

Barman58 said:

...

The result of your failure scenario would depend on the nature of your backups

if the daily backups are incrementally linked to your weekly backup, ie. they backup changes from the last weekly backup then you could loose the first days changes (when the weekly was run but not the daily ), if the Daily backups are run every day, and re-set weekly, you should be able to reconstruct all data as long as each daily backup includes all changes from the reset point, rather than just the daily changes.

Thanks for your answer. The daily backups are incremental.
But the part in bold. Do you actually mean "when the daily was run but not the weekly"?

Barman58 · 26 Mar 2013

Sorry for any confusion, In a daily / Weekly backup set it is possible that the running of a weekly means that the daily is not actually run on that day.

When running backups on a large database system I would always use 24 tapes! - seven daily tapes, five weekly tapes, ( to cover the five week months), and twelve monthly tapes - the monthly tape was always a new one with the old one being placed into long term storage, on a regular basis a daily tape replaced and was recycled to a weekly tapes and a weekly tape to a monthly so that no tape was used beyond a certain age this was due to the mission critical nature of the data, and the legal requirement to retain business data for seven years and would likely be overkill for most purposes :)