Chapter 12. Backing Up and Recovering the Database
A recent news story reported that a company suffered grave financial losses because a disgruntled employee destroyed the entire company's information system. The company spent many weeks and millions of dollars to recover their system. The company had viewed their backup strategies as "adequate" but had not tested their recovery plans thoroughly. When disaster occurred and they tried to recover their data, they found they could not recover all the files they needed. Their standard procedure had been to keep their backup data for one month and then reuse the tapes for new backups . In attempting to recover their data, though, they found that they had to go back further than one month. The data they needed was no longer available.
Even with rigorous security, a company can be vulnerable to data loss. One of the best policies a company can follow is to take a proactive stance in determining what forms of backup will be used to help ensure that the system can be successfully recovered. No matter what form of backups you choose to implement, we recommend you thoroughly test your recovery procedures to ensure that:
You know how to perform all forms of recovery with confidence.
You have completely analyzed your backup and recovery strategies.
You can successfully read your tapes on different tape drives from those used to make them.
The third point is very important. If you have created your backup tapes on one type of tape drive, you might not be able to read them from any other tape drive. One DBA we know intentionally "loses" a tablespace datafile from his system about once a month and has his data center recover that file to ensure that random files can be recovered successfully he insists they test recovery on the same type of drive and also a different one from the one on which the files were created. If the file can only be recovered from one specific tape drive (perhaps because the tape heads are slightly out of alignment), you may not be able to recover your system when you really need to.
Backup and recovery aren't only technical operations. Corporate management, as well as all systems support staff, must be made to understand the various forms of backup and recovery available. Since there are significant tradeoffs both in time and in the amount of data that can be recovered from the various forms of backup and recovery discussed here, you need to paint a clear picture to ensure that everyone understands the ramifications of choosing one form of backup over another.
In this chapter we'll briefly present an overview of the backup and recovery options available to the DBA. Because Oracle8 is new to many DBAs and because it presents some different backup and recovery choices, we'll first examine the various forms of backup available to the Oracle DBA, then follow with a discussion of what has been changed or is being provided in a different way for Oracle8.