RE: redo log file setup with mirrored drives

> -----Original Message-----
> We hope by
> eliminating redo log multiplex, but with OS mirroring we
> can speed up this loading process.

We deal with this by:

1. Hardware mirroring of archives.
2. Archives go to device on which no other I/O is present and, if there is a difference in the speed of devices in the system (for example 7200 rpm drives and 10000 rpm drives), the archives get the faster drives.
3. Alternating online redo between different devices, the theory being that when a log switch occurs then the log being archived will be on a device that is not being written to, so (we hope) the reads from that device will be faster.

Even after making the archiving as fast as possible, you still might be required to have a very large amount of online redo available in order to handle the backlog built up during peak times. We have found that archiving is so much slower than online redo writing in a case like this, that we can Oracle multiplex online redo to hardware RAID (redundant redundancy) and the archiving will still be the slow point.

I wouldn't worry about the fault tolerance aspect of online redo mirroring, since whatever would blow away both sides of a hardware or OS mirror would also blow away both sides of Oracle multiplexing. However, my experience has shown that, as far as any debate on how one mirrors online redo the point is moot. My experience is that, in this scenario, the archiving is what will snag things.

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-- 
Author: Stephen Lee
  INET: slee_at_dollar.com

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