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Oracle Tips by Burleson |
Oracle and Disk Usage
One of the
major arguments against relational database systems has been speed.
It has been said that relational systems are slow. It has been
found, however, that with proper tuning of Oracle applications and
operating system, as well as proper file placement, Oracle
performance is excellent. In fact I have seen Oracle8i deliver
subsecond response times even when searching tables containing
billions of rows (yes, I said billions.) Conversely, if you try to
place Oracle on an insufficient number of disks, performance will
suffer.
How Many
Is Enough?
Some
applications will do fine with two disks or volumes. This setup is
not great, mind you, but the system will function. Other
applications, such as large complex systems involving numerous
indexes, data tables, and tablespaces, may require dozens. To reduce
disk contention and maximize database reliability, it is suggested
that the Remote DBA utilize OFA procedures to place database files. The
next subsections cover file placement for some basic disk array
layouts.
One Area
(Surely You Jest)
It is
foolish and very dangerous to even consider using a single area to
hold all Oracle files for other than DOS, OS/2, WINDOWS NT, or
MAC-based single-user databases. Unless you have the latest and
greatest EMC array with multiple gigs of storage, hot replacement of
disks, and RAID5, a single large area can lead to problems. A single
disk failure or crash in a stripe set could completely destroy your
system. Since there are no file placement options with one area,
let’s go on to the next configuration.
Two Areas
(Just Barely Adequate)
At least
with two areas you can achieve separation of data and indexes and
can separate redo logs from archive log files. This gives you some
redundancies in recovery options. The file placement is shown here.
AREA1. Oracle executables, index datafiles, redo logs, export files,
a copy of the control file
AREA2. Data-datafiles, rollback segment datafile, temporary user
datafiles, archive log files, a copy of the control file
As you can
see, an attempt is made to spread I/O between the two areas. Indexes
and data are on separate controllers, as are redo logs and rollback
segments. Additional recoverability in case of disk crash is given
by having exports on one drive and archive log files on the other.
While infinitely better than only one area, having only two areas is
still an extremely vulnerable condition and is not recommended.
Again, with the most up-to-date storage areas with large caches,
extreme striping, and hot replacement of disks, one or two areas is
workable.
See Code Depot
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