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Differential Backup


Differential Backup

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GTR
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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!
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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.


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crazy4sql
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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 :-D
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
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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

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

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Ashish
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Bru Medishetty (2/10/2010)
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.



I Knew that, but diff backup takes almost same time and space as full backup again it depends (I was refereing if it was almost same size).

EnjoY!
Bru Medishetty
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GT-897544 (2/15/2010)
Bru Medishetty (2/10/2010)
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.



I Knew that, but diff backup takes almost same time and space as full backup again it depends (I was refereing if it was almost same size).



I had never seen a differential backup (worth a 7 days of data) being equal in size with the full backup size.. Can you quote under what conditions would that be equal (with respect to the scenario I mentioned or with your own example)


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Robert Davis
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If your differential backup is almost the same size and takes almost the same amount of time, then almost your entire database is getting updated in between. If you are experiencing htis, then you have soemthing wrong with your system or you're not taking the backups frequently enough.

What is the backup schedule?



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