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I have a setup for a customer whereby a full backup is conducted on a Friday - then Monday through to Thur, differentials are carried out. Now, there is a single media set for these two jobs (I understand that is obviously not the best way, if even a good way, of doing this, but, the customer uninstalled Backup Exec without recording his original setup, but wants it back exactly how he had it, I'm just confirming that a certain event won't occur) which both the Full and Differential will backup to.

Now in terms of the overwriting - the full is set to overwrite the media, since it runs once a week, I always want it to overwrite the previous weeks Full. But the Differentials are too going to the same media set. Now, obviously as they are differentials, I want them to always overwrite the previous days differential, so I have set them to Overwrite media when the job begins.

But, does this mean the Monday Differential will go ahead and start to overwrite the full backup from Friday, or will it not because the Full and Differential are two separate jobs?

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3 Answers 3

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hmallet is right...however:

Since your question seems to state that you have to use a single media set...yes, you would be overwriting the FULL with the first DIFFERENTIAL that takes place.

If there's enough room on the media, the best bet is to set the media set's Overwrite protection period to 6 days as hmallet has said, and set the Append period to 1 year (or anything longer than 6 days).

This would allow the backups to write a FULL backup and then up to 6 differentials to the same media, then it would overwrite again on the next FULL...repeat.

NOW, if there's not enough room on the media for a FULL and 6 differentials, then you need to consider doing what hmallett recommends and using multiple media and media sets. OR, you can switch to a FULL and INCREMENTAL method instead of DIFFERENTIALS....after all, you are only keeping a week's worth regardless on a media, so restoring a FULL then incrementals won't be that bad at all.

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If your media set isn't set to be overwrite protected any data on it can be overwritten by any job using that media set. So, yes, your differential could potentially overwrite your full backup. In order to accomplish what you want to, you would need to have the jobs on separate media sets. Is there a reason you are overwriting the previous day's differential job? Keep in mind that there is certainly the possibility of someone modifying a file two days in a row, and needing the copy from the first day. If you overwrite every previous day's differential job, that file would be lost.

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Whether a backup job overwrites a previous backup depends upon how your media sets are configured. Backup Exec doesn't care whether the previous backup on any media was a full or a differential backup.

Each Media Set in Backup Exec has an Overwrite Protection Period. You can find this information in the Media view, under the properties of the Media Set. The Overwrite Protection Period defines the minimum age any data on that medium may be before the medium is overwritten.

It is a generally a good idea not to overwrite the previous backup. (What happens if the backup fails - you don't have the previous one to go back to). However, I'll assume that that's definitely what you want to do.

In your situation, the best thing to do would be to create two media sets: one called Weekly Backups; one called Daily Backups. Set the Overwrite Protection Period on the Weekly Backups Media Set to 6 days. This allows any data on that media to be overwritable 6 days after the backup completes - if you set it to 7 days, it won't be overwritable by the time the next backup starts. Set the Overwrite Protection period on the Daily Backups to something arbitrary, like 1 hour.

Target your Full Backup to the Weekly Backup media set, and the Differential Backups to the Daily Media set.

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