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Oracle Tips by Burleson

Disk I/O Tuning

Chapter 4: Disk Stripping

Figure 4-1: Example of Disk Striping

Disk Shadowing or Mirroring 

If you have mission-critical applications that you absolutely cannot allow to go down, consider disk shadowing or mirroring. As its name implies, disk shadowing or mirroring is the process whereby each disk has a shadow or mirror disk that data is written to simultaneously. This redundant storage allows the shadow disk or set of disks to pick up the load in case of a disk crash on the primary disk or disks; thus the users never see a crashed disk. Once the disk is brought back on-line, the shadow or mirror process brings it back in sync by a process appropriately called “resilvering.” This also allows for backup since the shadow or mirror set can be broken (e.g., the shadow separated from the primary), a backup taken, and then the set resynchronized. I have heard of two, three, and even higher mirror sets. Generally, I see no reason for more than a three-way mirror as this allows for the set of three to be broken into a single and a double set for backup purposes. Shadowing or Mirroring is RAID 1.

The main disadvantage to disk shadowing is the cost: For a 200-GB disk farm, you need to purchase 400 or more gigabytes of disk storage. Figure 4-2 shows disk mirroring. In figure 4-2 disk group A is considered the active group, disk group B is the "mirror" group. Both disk group A and disk group B are maintained through simultaneous writes.

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

  • Guru support for your Oracle DBA

  • Installation of Oracle application packages

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