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Oracle Tips by Burleson

Disk I/O Tuning

Chapter 4: RAID—Redundant Arrays of Inexpensive Disks 

advantages as shadowing and striping at a lower cost. It has been suggested that if the manufacturers would use slightly more expensive disks (RASMED—redundant array of slightly more expensive disks) performance gains could be realized. A RAID system appears as one very large, reliable disk to the CPU. There are several levels of RAID to date: 

  • RAID 0. Known as disk striping.

  • RAID 1. Known as disk shadowing or mirroring.

  • RAID 0/1. Combination of RAID0 and RAID1. May also be called RAID 10 depending on whether they are striped and mirrored or mirrored then striped. It is generally felt that RAID 10 performs better than RAID 01.

  • RAID 2. Data is distributed in extremely small increments across all disks and adds one or more disks that contain a Hamming code for redundancy. RAID 2 is not considered commercially viable due to the added disk requirements (10 to 20 percent must be added to allow for the Hamming disks).

  • RAID 3. This also distributes data in small increments but adds only one parity disk. This results in good performance for large transfers, but small transfers show poor performance.

  • RAID 4. In order to overcome the small transfer performance penalties in RAID3, RAID4 uses large data chunks distributed over several disks and a single parity disk. This results in a bottleneck at the parity disk. Due to this performance problem RAID 4 is not considered commercially viable. RAID 3 and 4 are usually are used for video streaming technology or large LOB storage.

  • RAID 5. This solves the bottleneck by distributing the parity data across the disk array. The major problem is it requires several write operations to update parity data. The performance hit is only moderate, and the other benefits may outweigh this minor problem. However the penalty for writes can be over 20% and must be weighed against the benefits.

  • RAID 6. This adds a second redundancy disk that contains error-correction codes. Read performance is good due to

The above text is an excerpt from:

Oracle Disk I/O Tuning
Disk IO Performance & Optimization for Oracle Databases
ISBN 0-9745993-4-4 

by Mike Ault

Oracle Consulting Services

Burleson Oracle Consulting offers Senior Oracle consultants which are available for all areas of Oracle support.  Common Oracle consulting support activities include short-term Oracle tuning, Oracle database troubleshooting, Oracle9i and Oracle10g migration, Oracle9iAS App Server consulting, Oracle design reviews and Oracle requirements evaluation support. Oracle support and Oracle consulting services are priced by the hour, so you only pay for what you need. These one-time Oracle consulting services commonly include:

  • Answering questions from your Oracle DBA technical staff

  • Repairing down production Oracle database systems

  • One-time Oracle tuning evaluation

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  • Installation of Oracle application packages

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