Chapter 12: Back Up Database (Full) Task 161 also that the full database backup job will be completed before people come to work in the morning. As you can see, there are a lot of assumptions being made, and this is why I referred above to this discussion as being dicey. As discussed in Chapter 4, when you schedule jobs using the Maintenance Plan Wizard, you have to take an initial guess as to when a job should run so that it doesn't interfere with other jobs. Once you have tested your jobs, and also run them for a few days, you will get a better feel for how good your assumptions were. If they were wrong, you will then have to change the various scheduled jobs so that they "fit" better together. You will learn how to change a Maintenance Plan schedule in Chapter 19, on the Maintenance Plan Designer. Another thought may have occurred to you during this discussion: is it possible to schedule the daily full backup job at a specified time Monday through Saturday, and then at a different time on Sunday, so as not to interfere with the weekly Sunday maintenance jobs? Yes, it is, but it is at this point that the Maintenance Plan Wizard falls short, as it does not allow you to set multiple schedules for a single task within the same Maintenance Plan. The work-around for this is to create multiple Maintenance Plans, each with their own independent schedules. Another option is to use the Maintenance Plan Designer, which allows greater flexibility than does the Wizard. In other words, what I am saying is that, if you want to perform tasks that are not easily done from within the Wizard, such as creating multiple schedules for the same task, then you should probably consider using the Maintenance Plan Designer to create your Maintenance Plans, or using T-SQL or PowerShell scripts instead. Summary Of all the maintenance tasks you perform, the most critical one is the Backup Database (Full)task. Performing regular full backups is the only way you can guarantee that your data is protected should the original database become unavailable. On the other hand, the Backup Database (Full)task is not the only backup task you need to perform regularly. In the next two chapters, we will take a look at two other backup-related tasks. 162 Chapter 13: Back Up Database (Dierential) Task As you can guess by its name, this task is designed to create differential backups, in other words, to back up all changes in a database since the last full backup. Performing differential backups is not a substitute for making regular transaction log backups. If your databases are in the full recovery mode, transaction log backups must be included in your overall backup strategy alongside full backups and any differential backups. For reasons that will become clear as we progress through the chapter, I generally avoid performing differential backups if I can, preferring to rely on a combination of full and transaction log backups. Furthermore, if your database maintenance requirements do include performing differential backups, then I recommend that you create your Maintenance Plans using the Maintenance Plan Designer (see Chapter 16 onwards), rather than the Wizard. An Overview of the Back Up Database (Dierential) Task Since differential backups only copy the data that has changed since the last full backup (called the differential base), a differential backup is smaller than a full backup, so the nightly backup process is faster. However, as each day of the week passes, the differential backup will take longer to perform, as more and more data changes in the database. When the Backup Database (Differential) task runs using its default settings, it executes the following T-SQL code (assuming AdventureWorks is being backed up): BACKUP DATABASE [AdventureWorks] TO DISK = N'C:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\Backup\ AdventureWorks_backup_2009_08_19_154600_2850000.bak' WITH DIFFERENTIAL, NOFORMAT, NOINIT, NAME = N'AdventureWorks_back up_2009_08_19_154600_2830000', SKIP, REWIND, NOUNLOAD, STATS = 10 This BACKUP DATABASE command is virtually identical to the one we saw in the last chapter, for the Backup Database (Full) task, the only real difference being the addition to the command of the DIFFERENTIAL keyword. Unfortunately, the name assigned to the differential backup file looks exactly like the name of Chapter 13: Back Up Database (Differential) Task 163 a full backup (other than the date stamp), making it dicult to distinguish full backups from differential backups. To keep track, take note of the time stamp for the differential base file (last full backup) and then identify subsequent differential backup files from there. When a Backup Database (Differential) task runs, it produces a text report similar to the following: Microsoft(R) Server Maintenance Utility (Unicode) Version 10.0.2531 Report was generated on "HAWAII." Maintenance Plan: MaintenancePlan Duration: 00:00:00 Status: Succeeded. Details: Back Up Database (Differential) (HAWAII) Backup Database on Local server connection Databases: AdventureWorks Type: Differential Append existing Task start: 2009-08-19T15:54:39. Task end: 2009-08-19T15:54:39. Success Command: BACKUP DATABASE [AdventureWorks] TO DISK = N''C:\ Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\ Backup\AdventureWorks_backup_2009_08_19_155439_1450000.bak'' WITH DIFFERENTIAL , NOFORMAT, NOINIT, NAME = N''AdventureWorks_back up_2009_08_19_155439_1450000'', SKIP, REWIND, NOUNLOAD, STATS = 10 GO As you can see, the text report above is also virtually the same as the report for the Backup Database (Full), other than the references to "differential." If more than one database were having a differential backup, then you would see each of them in the report. When and How Often to Perform Dierential Backups Personally, I avoid differential backups, preferring to perform daily full backups, plus periodic transaction log backups. I find this process simpler and less confusing than combining full, differential, and transaction log backups as part of my backup plan. Chapter 13: Back Up Database (Differential) Task 164 Of course, there are reasons why you might want to incorporate differential backups in your Maintenance Plan. The most common reason given to use differential backups is when databases are very large, and taking a full backup each night is too time-consuming. What some DBAs do in these cases is to take a full backup once a week, and take differential backups for the remaining days of the week, while also incorporating transaction log backups. This reduces the amount of time each day it takes to perform a backup. On the other hand, as the week progresses, the differential backup time will get longer and longer, as data is changed in the database, negating some of the time savings provided by using differential backups. Only by experimenting will you know for sure if using differential backups is a good solution for your particular environment. Configuring the Back Up Database (Dierential) Task Let's examine the Define Back Up Database (Differential) Task screen from the Maintenance Plan Wizard, shown in Figure 13.1. The available options are the same as those seen and described for the Backup Database (Full) task in the previous chapter, so I'll refer you there for the details and will keep the explanation here short. The Backup type option at the top of the screen is automatically filled in by the wizard, and displays Differential. Database Selection and Backup Component If you decide to perform differential backups, you'll have to give the following question some thought: do you want to perform differential backups on all the databases on your server, or just some of them? In the context of the Wizard, differential backups can quickly trample over our goal of simplicity. Our aim throughout the book has been to apply each task to the same set of databases. So ideally, in the content of our running example, we'd select to apply differential backups to all user databases. Chapter 13: Back Up Database (Differential) Task 165 Figure 13.1: Creating and scheduling a differential backup task is virtually identical to taking a full backup. . AdventureWorks is being backed up): BACKUP DATABASE [AdventureWorks] TO DISK = N'C:Program FilesMicrosoft SQL Server MSSQL10.MSSQLSERVERMSSQLBackup AdventureWorks_backup_2009_08_19_154600_2850000.bak'. 2009-08-19T15:54:39. Success Command: BACKUP DATABASE [AdventureWorks] TO DISK = N''C: Program FilesMicrosoft SQL Server MSSQL10.MSSQLSERVERMSSQL BackupAdventureWorks_backup_2009_08_19_155439_1450000.bak''. text report similar to the following: Microsoft(R) Server Maintenance Utility (Unicode) Version 10.0.2531 Report was generated on "HAWAII." Maintenance Plan: MaintenancePlan Duration: