RE: redo log file setup with mirrored drives

Sure...

What I posted came from my discussions with others and from various resources on Metalink and from Oracle Training Classes. Note #45042.1 titled Archiver Best Practices summarizes it all.

Agreed, that RAID and disk technologies have improved over the years, however, I would still continue using multiple redo log members on any OS. Redo log files serve different purpose in an Oracle database, and so should be treated differently.

• Kirti

-----Original Message-----
Sent: Tuesday, November 26, 2002 9:24 AM To: Multiple recipients of list ORACLE-L

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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