RE: redo log file setup with mirrored drives

From: Rachel Carmichael <wisernet100_at_yahoo.com>
Date: Wed, 27 Nov 2002 07:54:06 -0800
Message-ID: <F001.0050D972.20021127075406@fatcity.com>

> I was amazed at the non-security that seems to be rampant out there,
> with mischievous people running around deleting files. I kept
reading
> about it and thinking you've got to be kidding.

Steven,

have you NEVER accidentally, at 3AM, after having been woken from a sound sleep to a crisis that needs to be fixed RIGHT NOW, made a typo?

if not, wow, I'm in awe. All you need to do is forget which directory you are in... and not include the path when do you an "rm". I've done it. I've learned to ALWAYS do a "pwd" at the OS level and a "select * from v$database" when I am connected to a database.

In any case, in another post you asked if anyone had ever lost a database due to hardware mirroring.

Um, I have. Okay, we recovered the database via Data Unloader, but essentially it was lost, because we couldn't open the database. The current redo log and its hardware mirror failed. To this day, I don't know why, there was a lot of finger pointing going on, including "you mirrored it onto itself" and "you had both disks on the same controller and it failed".

Regardless of WHY it happened, it happened. We could not switch the current log, we could not open the database, we couldn't access anything.

Tech support finally mentioned that there was this product that field support had...

and two DAYS later I had a database again.

In this case, Oracle mirroring (no, we were not using multiplexed redo logs) would possibly have saved us time, money and I might have had a few less gray hairs.

Rachel

• Stephen Lee <slee_at_dollar.com> wrote:
  > > -----Original Message-----
  > > We do redo log file multiplexing to protect against fat
  > > fingers and other odd-ball stuff that have caused problems
  > > for an entire file system. Call it an unreliable OS, poor SA
  > > (ok, maybe even DBA) practices
  >
  > I do it because it's a CYA thing of doing it by the book. I've
  > listened to
  > a lot of debates about database things and been amazed at the
  > reasoning
  > behind why people do what they do. I've lost count of how many
  > debates I've
  > heard about extent sizes and numbers of extents, the majority of it
  > pure
  > superstition. In the end, no matter how scientific or superstitious
  > the
  > reasoning, CYA trumps all. So that's why I do it. But, in fact,
  > this whole
  > thing about corrupt blocks is flawed reasoning. If an OS cannot do
  > disk
  > writes in an absolutely reliable way, then the OS is unusable. The
  > bad
  > writes will occur throughout the system. This includes when your
  > logs get
  > archived and writes to data files. Put those two together and what
  > do you
  > get?
  >
  > Actually, there is one advantage to hardware mirroring of archives.
  > On
  > Oracle duplexed archives, my experience is that it is inevitable that
  > you
  > will have one destination fill up while the other one doesn't. In
  > which
  > case Oracle quietly quits using the one destination even after the
  > files are
  > removed during a backup. I wrote a script to monitor when Oracle has
  > stopped duplexing archived logs for those where we don't have
  > hardware
  > mirroring.
  >
  > I was amazed at the non-security that seems to be rampant out there,
  > with
  > mischievous people running around deleting files. I kept reading
  > about it
  > and thinking you've got to be kidding.
  > --
  > Please see the official ORACLE-L FAQ: http://www.orafaq.com
  > --
  > Author: Stephen Lee
  > INET: slee_at_dollar.com
  >
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Rachel Carmichael
  INET: wisernet100_at_yahoo.com

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Received on Wed Nov 27 2002 - 09:54:06 CST