A backup question....

Hi, i was just wondering if you could tell me the answer to this question?

'You run normal backups every saturday and differential backups on tues & thurs to backup each member server (three servers) each backup operation will be stored on a seperate tape.'

What does this strategy allow for?

a) recovery using one backup tape
b) recovery using two backup tape
c) the quickest restore
d) the quickest backup

Thanks in advance.

Regards

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Comments

royal

b. Differentials back up everything since the last full restore. The differential backup does not modify the archive bit and that is why it backs up everything since last full backup. Because of that, when you go to restore, you restore last full backup and the latest differential.

pyroflames

a) recovery using one backup tape - Normal Backup Every Day
b) recovery using two backup tape - Normal Backup One Day and Diff the rest
c) the quickest restore - I would say Normal Backup, because you dont need to change drives...
d) the quickest backup - One Normal Backup and Incremental rest of the week.

UncleCid

Does differential affect incremental? Could you use incremental for the whole week, but have a differential in the middle? So in a nutshell, effectively use your full back up, then a differential, then the incrementals after that differential?

fullbackup->differential->following incrementals

pyroflames

ok, if you did that:

Monday - Normal
Tuesday - Incremental
Wednesday - Diff.
Thursday - Incremental
Friday - Incremental

Now in theory, if you server failed on friday afternoon after the backup:

You would need to restore:

Monday - Normal
Wednesday - Diff
Thursday - Incremental
Friday - Incremental

That would restore the server back to how it was at time of backup.

undomiel

Ok so for your idea of running an incremental in the middle of the week and then restoring you would restore full follow by the incrementals. The differential is of no consequence because it does not reset the archive bit so therefor the incremental after it would restore all that the differential had backed up. The differential only backs up what has the archive bit set. Since incrementals clear the archive bit it would only back up what has changed since the last incremental. Since differentials do not clear the archive bit the next incremental backup would backup everything the differential backed up plus the changes since the differential. That's why when restoring there would be no need for the differential backup at that time since the incremental after it has all the necessary changes.

pyroflames

The presense of the archive bit (if it is set) indicates that the file has been modified or created since the last backup. When the file is backed up, the backup software clears the archive bit. The archive bit is used when making differential or incremental backups.

A differential backup by definition is a backup method that backs up files that have been modified or created since that last full or incremental backup. During a differential backup, the backup software determines whether or not a file needs to be backed up by looking at the archive bit. If the archive bit is set, then the file is backed up. Differental backups do not clear the archive bit, so the file will again be backed up during the next differential or incremental backup but before the next full backup.

An incremental backup by definition is a backup method that backs up files that have been modified or created since the last full or incremental backup, including files that were modified before and after any differential backups. The incremental method backs up files that have the archive bit set, then clears the archive bit.

It is generally not a good idea to mix incremental and differential backups because it can be difficult to predict which archive set contains a particular version of a file. Also, it's not a good idea to mix backup systems because the resetting of the archive bit can result in undesired skipping of files during backup. Some systems allow you to specify that you don't want the archive bit reset during a full or incremental backup, or that you DO want it reset during a differential backup.

https://www.backupcheckup.com/modules/AMS/article.php?storyid=31

undomiel

pyroflames wrote:

You would need to restore:

Monday - Normal
Wednesday - Diff
Thursday - Incremental
Friday - Incremental

That would restore the server back to how it was at time of backup.

I would have to disagree on tha tone. You would need to restore Tuesday's incremental instead of Wednesday's differential because Thursday's incremental covers Wednesday but the differential does not cover Tuesday.

UncleCid

Well, i was hoping maybe it could make the incrementals a little less annoying without having to put a full backup. I guess it's not so bad since you don't have to restore all the time.

pyroflames

Wouldnt diff. cover tuesdays? Incremental doesnt reset the achive bit

pyroflames

UncleCid wrote:

Well, i was hoping maybe it could make the incrementals a little less annoying without having to put a full backup. I guess it's not so bad since you don't have to restore all the time.

Sorry been reading up

Normal Backups

All selected files and folders are backed up. The archive attribute is cleared. A Normal backup does not use the archive attribute to determine which files to back up; all selected items are transferred to the destination media. Every backup strategy begins with a Normal backup that essentially creates a baseline, capturing all files in the backup job.
Normal backups are the most time-consuming and require the most storage capacity of any backup type. However, because they generate a complete backup, normal back-ups are the most efficient type from which to restore a system. You do not need to restore multiple jobs. Normal backups clear the archive attribute from all selected files.

Incremental Backups

Selected files with the archive attribute set are backed up. The archive attribute is cleared. Selected files with the archive flag are transferred to the destination media, and the flag is cleared. If you perform an incremental backup one day after a normal backup has been performed, the job will contain only the files that were created or changed during that day. Similarly, if you perform an incremental backup one day after another incremental backup, the job will contain only the files that were created or changed during that day.
Incremental backups are the fastest and smallest type of backup. However they are less efficient as a restore set, because you must restore the normal backup and then restore, in order of creation, each subsequent incremental backup.

Differential Backups

Selected files with the archive attribute set are backed up. The archive attribute is not cleared. Because a differential backup uses the archive attribute, the job includes only files that have been created or changed since the last normal or incremental backup. A differential backup does not clear the archive attribute; therefore, if you perform differential backups two days in a row, the second job will include all the files in the first backup, as well as any files that were created or changed during the second day. As a result, differential backups tend to be larger and more time-consuming than incremental backups, but less so than normal backups.
Differential backups are significantly more efficient than incremental backups as a restore set, however. To fully restore a system you would restore the normal backup and the most recent differential backup.

Just dont mix up backups, they shouldnt ask....