Tip

Choose the right RAID level

This tip courtesy of SearchWinSystems.com.

Because of their size and complexity, database management system installations can frequently benefit from using different RAID levels to support various parts of the system.

Oracle

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Corp. recommends using the following RAID levels for different components of an Oracle 9 or 10 installation:

  • Operating system -- RAID 1.
    Oracle suggests using RAID 1 (mirroring) for the disk holding the operating system and Oracle binary files. In the event of failure, it's much easier to restore the OS and binaries than to rebuild the volume using something like RAID 5. This cuts down the time necessary to restore the system.
  • Redo log files -- RAID 1 or RAID 10.
    These files are sequential rather than random, so RAID 1 or RAID 10 (striping and mirroring) provide better performance than RAID 5 (striping with distributed parity). These files are also small enough that the higher cost of RAID 10 isn't a major factor.
  • Data files -- RAID 5 or RAID 10.
    The key here is a combination of cost and ratio of reads to writes. RAID 5 is significantly less expensive than RAID 10, but because of the differences in write performance, RAID 5 extracts a performance penalty. Oracle recommends using RAID 10 if fewer than 90% of the I/O operations are reads. If more than 90% of the operations are reads, then RAID 5 is an acceptable option. Of course, because of the cost penalty associated with RAID 10 (the need for twice the disk capacity as the amount of data storage), some installations will go with RAID 5 for cost reasons and accept the performance hit.
  • Archive log files -- RAID 10 or RAID 5
    . Here again, RAID 10 will give better performance, but the penalty associated with RAID 5 in writing and rebuilding a failed drive may be slight enough that RAID 5 is acceptable.

Installing Oracle databases on Windows systems is discussed in a joint white paper from Oracle, Microsoft and Dell Inc., "Deployment Guide: Oracle on Microsoft Windows and Dell PowerEdge Servers," which is available on Dell's Web site (www.Dell.com). As the title implies, the paper is specific to Dell servers, but the information is generally useful to anyone installing Oracle on Windows.

Reader feedback

Don B. writes: "Oracle's standard for RAID is SAME (Stripe and Mirror Everywhere), so this article is wrong and VERY misleading. For more info, check out BAARF, the "Battle against any RAID Five," at http://www.baarf.com/ ."

Mark G. writes: "I'm surpised in the author did not mention the temp or undo tablespaces. In my experience, they both get more I/O than then other parts of the database combined. I recommend RAID 1 or 10 for undo and RAID0 or non-RAID for temp (as well as for the Windows swap file)."

About the author

Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in storage and other computer issues.

This was first published in July 2005

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