I setup a SQL Server maintenance plan as follows:
Full backup every Sunday at 2am
Differential backup every 3 hours
After the full backup was taken, I noticed the differential backups are varying in size. At first it started out small and grew accordingly. However, at various points, some differential backup file sizes may be larger or smaller than before. This includes big differences (i.e. 200MB to 3MB). I know that no other full backups have been taken nor has any large amount of data been deleted during those times. What would be the cause and is there something I am missing? Based on the research I've done, the differential should do nothing but increase until another full backup is taken.
Any insight would be appreciated.
Thanks!
Are you talking about differential backup or differential partial backup? What you describe looks a lot like differential partial backup. Differential partial backup were introduced with MSSQL Server 2005 and are very similar to incremental backup.
With differential partial backups only the changes since the last partial differential backup are kept. That means two things :
the file size of differential partial backup will vary according to the amount of changes in the database since the last differential partial backup.
if you want to restore a backup you have to restore the full partial backup (the base) and then every differential partial backup file.
Here is a very complete and interesting article about MSSQL partial backup.
Edit
The terminology used is a little confusing. In Microsoft documentation it is called partial differential backup (even though it works pretty much like an incremental backup) and to do that you have to use the very intuitive READ_WRITE_FILEGROUPS flag. AFAIK, you have to use T-SQL commands like :
BACKUP DATABASE [SampleDB] READ_WRITE_FILEGROUPS
TO DISK = N'C:\SQLBackups\SampleDB_PARTIAL_Diff.bak'
WITH DIFFERENTIAL
GO
Related
I'm periodically getting backups of an SQL database which I would like to restore in my machine. I'm able to do that with RESTORE fullDB WITH NORECOVERY; RESTORE differentialDB WITH RECOVERY;
However, I need to access the restored database in between, as the interval in which I'm getting the backups can be a few hours.
I tried restoring full backup WITH RECOVERY, but in that case I'm getting exception while restoring differential backup.
NB: It's not just one differential backup, it's real time backups taken every few hours. I'm using C# for executing the operations.
Any help is appreciated to solve the issue. Also, let me know if I'm barking at the wrong tree.
Instead of sending SQL database backups from client as .bak files, should I opt any other way to send the data?
Take a look at the STANDBY option for the RESTORE statement. From the docs:
Specifies a standby file that allows the recovery effects to be undone.
NB - differential backups are based on the last full backup taken. So let's say that you take full backups on Sunday, differential backups every other day of the week and you're restoring every day.
Sunday, you'd restore only the full backup, bringing it online for read by specifying STANDBY with the restore
Monday through Saturday, you'd restore the latest differential backup on top of what you've already restored, again using STANDBY
When Sunday rolls around again, you'd need to restore the new full backup.
That said, you mentioned that you're on SQL Express. The database size limit is 10 Gb. At that size, how long does the restore of the full backup take? Is it worth your time? And even there, it's really "how much time are you saving the robot?" because you've already (presumably) automated the restore.
I'm using full backup which is scheduled daily. Each day changes has been done in big level so that i choose full backup. what will be the major changes if i choose copy only backup while taking the full backup ? Actually i need to speed up the backup process and how could the copy only back will be affect the actual full backup process?
Copy only backup are similar to full backup (they backup the entire database) however they won't have any impact on DatabaseBackupLSN. They will not speed up your backup process. You can consider differential backups to backup only the changed data which can be faster compared to full backup (unless entire data is changed).
I have SQL Server 2012, and a Backup drive apart, but it is really full. I want to move all the backups, after done, to a Network Drive. My concern is with the differential and log backups, as I don't know if they need to see the full backup to be done, or how does it works in SQL Server.
Is it safe to move the Full Backup to another drive, and then execute the daily differential backups?
Let us remember the golden rule for restoring first.
‘After restoring full database backup, restore latest differential database backup and all the transaction log backup after that to get database to current state.’
So if you have only one full backup and then keep on taking differential backup's the size of the differential backup will keep on growing everyday. In case of disaster you may have to find the older full backup and then restore the latest differential backup.
So in theory: If you take one full backup and move to somewhere else and keep on taking differential backup works.
However, there are changes that your full backup may get corrupted or your differential backup have issues. You will in that case miss another full backup.
It is always a good idea to take full backup at regular intervals. I take full backup of my databases every day when they are relatively small and every other day when they are very large.
Here is the blog post where I have written about backup timeline.
https://blog.sqlauthority.com/2009/07/14/sql-server-backup-timeline-and-understanding-of-database-restore-process-in-full-recovery-model/
To answer the question you asked, the SQL Server doesn't access the full backup itself when it makes differential and log backups. It instead keeps track of what needs to be backed up in the database itself.
The short version of that for differential backups is "the notion of what's changed (and therefore needs to be backed up) is kept track of in what are called differential change map pages" and for log backup is "the notion of what's changed (and therefore needs to be backed up) is kept track of in the transaction log itself".
The longer (and IMO more interesting) version is this excellent article by Paul Randal.
To recover, you need to restore the full backup before the differential. The normal recovery sequence is to restore the latest full backup, latest differential backup after the full backup, and log backups since the differential in sequence.
The backup files obviously need to be available in order to restore regardless of where you store them. If you were to lose the local full backup, you could not restore at all. You might consider copying the full backup to the network share as an extra layer of safety.
I have to create script which will create the database locally (from database which is on server). Database is 20GB+ and every day is bigger.
What is your advise to do that? I can generate script with all database objects in SSMS, but how operate with data insertion? I mean full script (script which includes data) is not good option. What about one Full Backup and Differetial Backups?
Run generated scripts for all DB objects
Restore Full Backup
Restore Differential Backup
This work is required in order to make possible to test the app locally, on my (another dev's) machine. Thank for every advise!
My advice is to go with a full backup first & get differential backups afterward.
Because a differential backup is not independent and it must be based on the latest full backup of the data. That means there should have a full backup as a base. A differential backup contains only the data that has changed since the differential base. Typically, differential backups are smaller and faster to create than the base of a full backup and also require less disk space to store backup images.
Therefore, using differential backups can save available space and also speed up the process of restoring. At restore time, the full backup is restored first, followed by the most recent differential backup.
I am working with a data warehouse with SQL Server 2012 and was wondering what would be the most optimized, automated procedure for a backup/restore strategy.
Current observations and limitations:
1) Cannot use transaction logs as it would affect my load performance - datasets are potentially huge with large transactions
2) Current plan is to do full backup every week and differential backup every day
I am not sure when DML operations will happen as it depends on my application's usage, but is there a way to just track the NUMBER of changes to a database that would trigger a differential backup? A way that would not affect performance? I do not want to be taking unnecessary differential backups.
Would Change tracking be a good solution for my scenario? Or would there be overhead involved? I do not need to know the actual data that was changed, just the fact that it was changed by a certain amount.
Thanks in advance!
Well, there's this ( http://www.sqlskills.com/blogs/paul/new-script-how-much-of-the-database-has-changed-since-the-last-full-backup/ ). I'm just trying to figure out what problem you're trying to solve. That is, if you find that the size is below some threshold, it will be (by definition) cheap to do.
It all depends on your DWH configuration.
1. Is your DWH database partitioned? If yes, It would be easier to do the daily db backup(diff backup) for the current partition ONLY. It's much more smaller set of data to be backed up.
If not, Current plan is to do full backup every week and differential backup every day is the only way since you cannot use transaction log file.
You could also try 3rd party disk (block) level backup software (i.e. Doubletake)....
Hope it helps.
You seem to have a mistaken notion of what a differential backup is. Don't worry; it's common.
When you say things like "track the number of changes to a database that would trigger a differential backup", it implies that you think that a differential backup gets all of the changes since the latest full or differential.
However, a differential backup gets all of the data that has changed since the last full backup only. So, you'd expect the size of subsequent differential backups to get larger and larger. For example, let's say you take a full backup on Sunday and a differential backup every other day. You'd get something like:
Monday: All of the data changed since Sunday's backup.
Tuesday: All of the data changed since Sunday's backup (including Monday's data)
Wednesday: All of the data changed since Sunday's backup (including Tuesday's data)
etc
Additionally, you'd only ever restore at most one differential backup if/when you need to restore your database. For instance, if your database crashed on right before Thursday's backup, you'd restore your last full backup (from Sunday in my example), then Wednesday's differential, and you're done.
As for when to schedule it, that's typically dictated by the rhythm of your business. For instance, you might decide to take a backup just before you kick off your ETL or just after. Doing it during doesn't make much sense as you'd have an inconsistent (with respect to your ETL process) database if you ever need to restore it.