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Donald K. Burleson
Oracle Tips |
Oracle Disk Layout
Is the disk a raw device (for
UNIX)? If the disk is a raw device, this restricts your capability
for file naming. Be sure you maintain an accurate log of tablespace
mapping to raw devices. Map tablespace and other asset locations
ahead of time. Remember, an entire raw partition must be used per
Oracle datafile; it cannot be subpartitioned without redoing the
entire raw setup. If you must use raw, plan it!
What is the speed of the disk? By speed of disk we are referring to
the access and seek times. The disk speed will drive disk
throughput. Another item to consider when looking at disk speed is
whether or not the disk is on a single or shared controller. Is the
DSSI chained? All of these questions affect device throughput.
Generally, datafiles and indexes should go on the fastest drives; if
you must choose one or the other, put indexes on the fastest.
Rollback segments and redo logs can go on the slowest drives as can
archive logs and exports.
Is the disk a RAM or an optical disk? Ultimately, the RAM and
optical usage ties back to disk speed. A RAM drive should be used
for indexes due to its high speed. It is probably not a good
candidate for datafiles due to the RAM drive’s current size
limitations; this may change in the future. An optical drive, due to
its relative slowness, is excellent for archives and exports, but
probably shouldn’t be used for other Oracle files. A possible
exception might be large image files (BLOBs) or large document
files. Usually, unless you have a rewritable CD system, the
tablespaces placed on a CD-ROM will be read-only. With the storage
capacities of most optical drives, they make excellent resources for
archive logs and exports. They can conceivably provide a single
point of access for all required recovery files, even backups. This
solves the biggest recovery bottleneck: restoration of required
files from tape.
This is an
excerpt by Mike Ault’s book “Oracle
Administration & Management”. If you want more current Oracle tips
by Mike Ault, check out his new book “Mike
Ault’s Oracle Internals Monitoring & Tuning Scripts” or
Ault’s Oracle Scripts Download.
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