Section 15.8. What Can Happen to an RDBMS?


15.8. What Can Happen to an RDBMS?

A lot of things can happen to interfere with the normal operation of a database. What you need to do to get the database running again will depend on what broke it in the first place. The following is a list of some of the things that can happen to an RDBMS:


Device ownership change

Someone can accidentally change the ownership of the raw devices or files that the database is using for datafiles. Since the database can no longer write to the files, it will cease to function. You will need to return the device to its proper ownership and possibly restore data.


Device permissions change

This is similar to an ownership change, because the database engine can no longer write to the file. The fix is the same as the previous one.


Disk destruction or failure

The only real protection against a bad disk is RAID or some type of backup or replication.


Logical corruption

A database can become logically corrupted in all sorts of ways. Deleting an important table is an example of logical corruption. The process of retrieving and storing pages can also result in logical corruption that can only be seen using a database consistency checker or an export.


Controller goes bad

If you are mirroring some of your devices, you should set up the mirroring so that a device on one SCSI controller is mirrored to a device on another SCSI controller. This ensures that if a SCSI controller does go bad it won't take out both mirrors at once.


Assign a database raw device as a swap or filesystem

This one's a bad one. This is where proper documentation comes in handy. It also helps if your administrators are trained to look at the ownership of a device before they use it. If it is owned by someone other than root, then don't use it. To recover from this, you need to undo the change and restore from backup.


Another application using the raw device as mirror

This is similar to the preceding scenario; an administrator tries to use one of the database disks for something other than the database. Again, you will have to undo the change and restore from backup.




Backup & Recovery
Backup & Recovery: Inexpensive Backup Solutions for Open Systems
ISBN: 0596102461
EAN: 2147483647
Year: 2006
Pages: 237

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