RE: redo log file setup with mirrored drives

  Addressing the corruption issue, Kirti's statement is not speculation. Because my OS/hardware IS reliable a corrupted log file that is mirrored outside of Oracle will be corrupt - the original is corrupt, so is the mirror. If I mirror my log files using Oracle, logfile A may be corrupt, but log file B may NOT be corrupt, depending on what caused the corruption (if it is some Oracle bug, then you're out of luck either way).   We had a case where all files that were open on a particular file system became corrupt. The cause was related to a bug in the cluster software during a system crash. This file system was RAID 0+1 - which meant that my file was "safe", corruption and all. Fortunately, I had Oracle mirroring the redo log on another file system which was unaffected by the crash.

Jay

>>> slee_at_dollar.com 11/26/02 10:23AM >>>

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.

**DISCLAIMER
This e-mail message and any files transmitted with it are intended for the use of the individual or entity to which they are addressed and may contain information that is privileged, proprietary and confidential. If you are not the intended recipient, you may not use, copy or disclose to anyone the message or any information contained in the message. If you have received this communication in error, please notify the sender and delete this e-mail message. The contents do not represent the opinion of D&E except to the extent that it relates to their official business.

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Jay Hostetter
  INET: jhostetter_at_decommunications.com

Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
San Diego, California        -- Mailing list and web hosting services
---------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).