Beginning Oracle Database 11g Administration From Novice to Professional

CHAPTER 4 PLANNING 75
destination before they can be reused. The amount of space required for the storage of
archived redo logs depends on the amount of activity in the database; it also depends on
retention preferences. An amount of space equal to the size of the database would not be
unreasonable for a busy OLTP database.
Backups and Exports
Allocating an area twice the size of the database for backups would not be an unreasonable
thing to do, unless you plan to put backups directly onto tape.
Software Executables and Related Files
Some space must be allocated for the Oracle software and for various categories of error
logs such as the alert log, listener log, and trace files. Four gigabytes of space is a reasonable
rule of thumb for most databases.
Other Disk Considerations
There’s more to worry about when it comes to files than just the amount of space they
will take. Usable space, file placement, and disk speed are some of the issues to consider.
Usable space
When specifying the amount of space required for the data, be clear that you are talking
about usable space. For data protection, most disks utilize some form of RAID (Redundant
Array of Inexpensive Disks) layout which reduces the amount of usable space.
RAID 10 (mirroring plus striping) reduce the amount of usable space by 50%. RAID 5 has
the most usable space but reduces write performance; the details are outside the scope
of this book. RAID 10 is the best choice for databases.
File Placement
Some attention must be paid to the placement of different categories of files; for example,
data files should not be placed on the same file system where software, archived redo
log files, or backups are stored. Optimal Flexible Architecture (OFA) is a set of recommendations
provided by Oracle for the placement of different categories of files. OFA is
automatically used by Database Configuration Assistant (DBCA) when creating databases.