RE: redo log file setup with mirrored drives

If I may offer another view ....

> -----Original Message-----
> Having multiple redo log members has its advantages. The
> archiver process 'knows' these multiple members and it will
> optimize the archiving process,

Is there any supporting documentation about this "optimizing"? Are you saying that the makers of hardware-based and software-based RAID have not "optimized" their RAIDing? If I were a betting man, I would bet that a hardware device can do mirrored writes faster than Oracle.

> but it does not know about
> the mirrored copies of these logs.

Know? What does it need to "know"? Mirroring is mirroring. A mirrored copy either exists, or it doesn't. "Knowing" about it has no effect on the existence of the copy. Computer operations aren't based on faith (although there are many times we are tempted to question that).

> The other important thing
> to know is that Oracle issues a separate write for these log
> members

And this improves performance?

> and in an unlikely event a corrupted write will be
> restricted to just the affected member. Such corruption will
> affect all the mirrored copies.

Two things:
1. This is pure speculation.
2. If your OS can't do reliable disk writes, then it's time to get a new OS. A database consists of more than just redo logs. It also has pesky little things like data files. Should we have Oracle mirror those too rather than rely on RAIDing for fault tolerance? Why would we expect the OS to reliably write data files and detect hardware errors when it can't reliably maintain redo logs?

Pending further evidence to the contrary, I'll take mirroring external to Oracle as the better choice.

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Author: Stephen Lee
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