There are several types of database corruptions that can cause extensive data loss if due diligence is not taken to prevent it from happening in the first place:
Datafile block corruption—physical or logical
Table/index inconsistency
Extents inconsistencies
Data dictionary inconsistencies
Physical corruption is most often caused by defective memory boards, power disruption, I/O controller problems, or broken sectors on a hard disk drive. A defective physical component prevents the complete write to the data block, which also includes the accompanying update to the header block. You may have block corruption, but the database will appear to operate normally because reads usually don't have an issue but writes will report the corruption error as something similar to the following:
ORA-01578: ORACLE data block corrupted (file # string, block # string)
Don't always expect issues such as corruption to show up in an obvious way. While doing testing for this chapter...
