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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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