Unix Backup and Recovery

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, since the database engine can no longer write to the file. The fix is the same as the previous one.

Removing device symbolic link

In Unix, you are well advised not to use the actual raw device when setting up a database. You should make a symbolic link to a name that makes sense (e.g., ln -s /dev/rdsk/c0t0d0s0 /dev/informix/chunk1). This allows for much greater flexibility if that device goes bad. However, you need to document what device the database is pointing to so that you can remake the link in case someone deletes it. (You also can restore this information from backup, but it would be much faster to remake it if you knew what to link it to.)

Disk goes bad

The only real protection against a bad disk is mirroring and backups.

Controller goes bad

If you are mirroring some of your devices, you should set up the mirroring so that a device ...