Backup: Differencial vs Full

[scott_417]

I would like to ask further about these two backup methods. If I use the differencial/incremental method, suppose Day 1's backup is 100 GB, DAY 2's change is 10 GB, so total will be 100 Plus 10 GB; Now for the full backup daily, DAY 1 is 100 GB, and Day 2 will be 110 GB.

The backup capacity is all the same. In the case of failure of the server, I can do the recovery from either backup's data. Then why do we use these two separate methods, and what are their advantage/usage?


Thanks to help.

Scott

[Uwe Zessin]

In case of 'incremental', day-2 only saves 10 GB, not 100+10 GB. That means a faster backup on day-2.

In case of 'differential', you only need the full backup and the latest diff to do a complete restore. You don't need to handle all incremental backups.

If one incremental backup media in the middle (e.g. day-1) is defective, you 'backup chain' is broken. It won't be that bad on differentials - all older diffs are not needed for a full restore, only the last one. If the last one is defective, you can still go to day N-1.

[Steven Clementi]

Scott:

If you have alot of data to back up and do not have the time to do Full backup all the time, then differential/incremental method with 1 day of full is usually an acceptable alternative.

With differential, only the files that have changed since the last full are backed up.

With incremental, only the files that have an archive bit turned on. Effectively, any file that has changed since the last backup of that particular file.

Exampple:

You do a full back up of 100GB of data on Friday. Monday night comes along and 5GB of that data has changed and 5GB was added. A Differential and Incremental would backup 10GB of data.

On Tuesday, another 5GB of different data changes and 5GB added. A differential would backup 20GB and an incremental would backup 10GB.

On Wednesday, another 5GB of different data changes and another 5GN is added. A differential whould backup 30GB (10 from nite 1, 10 from nite 2 and 10 from tonite). An incremental would ony back up 10GB.

This goes on for thursday as well.


Not, to restor the data....

If you did incrementals... You would restore the last full backup, then restore each incremental after that.

If you did differentials... You would restore the last full backup, then the LAST differential backup. I.E. Last Fridays full backup and this Thursdays Differential (if you were restoring on this Friday).


Using differential backups make the restore process easier, takign less time. They use more resources though to hold the extra data.

Using incremental backups male the restore process longer, but use up less resources.


Steven

[Uwe Zessin]

> Using incremental backups male the restore process longer,
> but use up less resources.

Yes, and what I forgot: if you need a single file from a given date it's faster from an incremental because the amount of data to walk through is smaller.


So, no matter which way you choose - there are good things and not so good things - the choice is yours ;-)