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diff backup - practical issues

Posted on 2011-02-18
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Last Modified: 2012-05-11
When does differential make sense? Because it has an overhead - it needs a FULL and a DIFF instead of just a FULL (plus trans log backups). Does this put stress on the tape backup team to track 2 backups (instead of one). is there sometimes chaos because both tapes are not available or one is overwritten.

Is there any time it does not make sense to do diff backups (because of extra overhead)

also does diff backup take 'more' time to comb through the entire DB for the changes that have taken place?

thanks
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Question by:anushahanna
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Accepted Solution

by:
rocky_lotus_newbie earned 125 total points
ID: 34929028
Faster Data Recovery - In a disaster scenario, it is easier to restore Full Backup + Latest Differential backup + any latest transaction log backups than restoring Full Backup + all the transaction log backups. IMO, this is the major advantage of DIFF backups.

Below link has more informations:
http://www.mssqltips.com/tip.asp?tip=1233

Thanks,
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LVL 32

Assisted Solution

by:bhess1
bhess1 earned 125 total points
ID: 34929056
Differential backups make sense depending on how long you have to restore in case of disaster, how often you create log backups, and how long you have between full backups.  Consider a strategy of Full backups every day at midnight, log backups every 10 minutes.  If your DB dies 10 minutes before midnight, you have to restore 1 full + 143 log backups + the current log file = 145 restored files to recover.  If, instead, you have a differential backup every hour on the hour, you need 1 full + 1 differential + 5 log backups + the current log file -- 8 files to recover.

you need to evaluate your needs to see what is needed for your system.
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Assisted Solution

by:Aaron Shilo
Aaron Shilo earned 125 total points
ID: 34931820
hi

the isue is pretty simple.

if you need backups (we all do) and you cannot backup all the complte database every day,
and you want to minimize the need of restoring from multiple files (and minimize the risk of loosing one of them) then what you do is create a backup plan that will serve you to the best way.

1.full backup once a week
2. log backups every 1 hour.
3. diff backup every night.

now at the end of every day all you need for recovery id the FULL backup and the last DIFF backup you can disregard all log files in the middle.

this will make thing much easier to maintain and faster to perform.
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LVL 23

Assisted Solution

by:Racim BOUDJAKDJI
Racim BOUDJAKDJI earned 125 total points
ID: 34933661
<<When does differential make sense?>>
Primarily in two cases:
> when you have databases that take too long to do a FULL backup on daily basis
> when you can't afford the retention on the daily size of a full backup.  

The differential backup is really a feature that optimizes space daily consumption and reduces daily backup windows.

<<3. diff backup every night.>>
You probably mean every night, except the one when the full backup is to be performed. ;)

hope this helps
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Author Comment

by:anushahanna
ID: 34935948
Thanks - helpful. I am pleased you all mentioned only good things about Diff backups..

what about the overhead topic I heard at times on Diff (it takes extra care to track diff+full instead of just full)

is there any circumstance where diff backup is a con or has negative implications?
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