By correctly fixing optimal size.
create rollback segment roll1tablespace roll1.
Whenever changes happened to the database previous change will be there in the rollback segment.
Hit Ratio is the ratio of shared SQL and PL/SQL items found in the Library Cache versus physical storage. It can also be defined in a mathematical expression as 1 - ((physical reads) / (db block gets + consistent reads)).
We should depend on export/import utility for backup/recovery (fully reliable) The tar command cannot be used for physical file backup, instead we can use dd command which is less flexible and has limited recoveries.