Differential Backup

Question

Differential Backup

crazy4sql

SSCoach

Points: 19590
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February 8, 2010 at 1:50 am

#141091

Hi Guys,
Just a quick question, is it advisable to have differential backup in production environment and what should be its frequency if you taking full backup daily midnight and log backup after every 15 min?
Regards
Ashish
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Ashish

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Dinesh Asanka SSChampion Points: 11058 More actions · Answer 1

in your senario, you don't need diff backups. But there are places which has only one full backup for a week. take diff. backup daily mid night. log backups during day time

My Blog: http://dineshasanka.spaces.live.com/

free_mascot One Orange Chip Points: 27169 More actions · Answer 2

Again it depends on how critical the data is and you need to justify taking differential backup.

In your environment taking differential backup will only help when you need to recover the data on production. It will help you to reduce the down time by reducing the restore of T-log backups.

HTH

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maechismo_8514 SSCoach Points: 17510 More actions · Answer 3

Dinesh Asanka (2/8/2010)
in your senario, you don't need diff backups.

That's a wrong piece of advise.

But there are places which has only one full backup for a week. take diff. backup daily mid night. log backups during day time

Totally depends on his business requirements and the recovery period that they have set to. Differential backups are an added advantage on database recovery at a DR scenario and also it does not lead to confusion. It is better and recommended to have atleast one differential backup during the mid-day.

crazy4sql SSCoach Points: 19590 More actions · Answer 4

Thanks for so quick response.

But my only point is running differential backup for big database and highly transactional database, will impact the performance....

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Ashish

U J SSCrazy Points: 2423 More actions · Answer 5

Adding additional differential backup on your existing backup policy may impact your performance(schedule it at non-peak hours).. and not to mention,you will have to preserve it to achieve the recovery..

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 6

Krishna Potlakayala (2/8/2010)
It is better and recommended to have atleast one differential backup during the mid-day.

Why?

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

maechismo_8514 SSCoach Points: 17510 More actions · Answer 7

GilaMonster (2/8/2010)
Krishna Potlakayala (2/8/2010)
It is better and recommended to have atleast one differential backup during the mid-day.
Why?

Woudn't be a better option to restore Full backup then differential which was taken during the mid day and then all subsequent transaction log backups, instead of going through those bunch of Tlogs for every 15 mins. 🙂

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 8

Maybe, maybe not.

Depends how big the DB is, how long it takes to backup full, diff or log, how long the restores take, what the downtime allowance of the DB is, how much storage space is available, how long backups are retained, how much of a performance impact the diff backup has, etc.

There's no absolute right or wrong answer.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

maechismo_8514 SSCoach Points: 17510 More actions · Answer 9

True Gail, completely agree on that. I dint want to complicate him and advised as a possible solution that he'd better has a differential backup during the mid day which may reduce some labor intensive work.

GTR SSCrazy Eights Points: 8007 More actions · Answer 10

I agree with Gail, but diff backup takes almost same time and space as full backup again it depends. Personally i would prefer full back every night and log backup once every hour, with SQL 2008 compression you will save lot of space on full backups.

EnjoY!

EnjoY!

Bru Medishetty SSC-Insane Points: 23606 More actions · Answer 11

GT-897544 (2/10/2010)
I agree with Gail, but diff backup takes almost same time and space as full backup again it depends. Personally i would prefer full back every night and log backup once every hour, with SQL 2008 compression you will save lot of space on full backups.
EnjoY!

I don't agree with you on the time taken for a diff backup. The time taken perform a Diff backup will be far lower than the time taken perform a Full backup. Since the differential backup backups only the changes since the last full backup it would be only backing up those modifications.

If there is a DB which is 450 GB (grown over a period of 2 years), and there are changes worth 1 GB for each day, the daily Diff backup will be of the size of that much (1 GB) on day one and tends to grow, since diff backups are cumulative. At any point it would be still be lower than the full backup.

And regarding, log backups every one hour, that needs to decided by the amount of data modifications since the transaction log file will keep increasing without log backups.

Bru Medishetty

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crazy4sql SSCoach Points: 19590 More actions · Answer 12

Thanks to all for their valuable update.

So what I understand is Differential backup is important but not hard and fast. What is important is your log backup must be at regular frequency as per your database size which will not only help to minimise the log file space on drive but also smallest the file, quickest to resote 😀

Also if required apply differential backup if full backup is taking too much cost of disk I/O and taking time...:w00t:

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Ashish

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 13

ashish.kuriyal (2/13/2010)
What is important is your log backup must be at regular frequency as per your database size

Frequency of log backups is not related to DB size. It's related to DB activity and the maximum amount of data that the business is willing to lose in a disaster.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

crazy4sql SSCoach Points: 19590 More actions · Answer 14

100% true... was isolated to my environment :w00t:

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Ashish