Subject: Re: differential scsi controllers
To: None <>
From: Tim Rightnour <>
List: current-users
Date: 07/01/1998 09:20:28
On 01-Jul-98 Thor Lancelot Simon spoke unto us all:
#  Even if it worked, it wouldn't be worth using.  It's absolute idiocy --
#  mirroring for the sake of being able to say you're mirroring.  It always
#  reads from the first component of a mirror set, thus giving no performance
#  benefit, and it doesn't handle errors *at all*, meaning that an error on
#  either component will cause the halves of the mirror to become inconsistent,
#  so that is very unlikely to provide redundancy, either.  It's Awful.  It
#  should have been removed Long Ago.

I hate to say it, but AIX has a really nice software mirroring.  If the drive
in question bites it, it does a few things:

A: It marks the partitions on the bad drive as being stale, and no longer
reads/writes them if a previous read/write failed.

B: Noticing a stale mirror, allows you to break that mirror, (without affecting
anything runnning on it)  Assuming you have a hot-swappable drive, you can then
throw it in, and resync the mirror, and go on with life.

Even if we dont have a hot-swappable media, it would be nice to be able to
break the mirror, and continue with life until the new drive arrives and we can
shut down.  No applications need to die until you actually shut the machine
off, and most importantly, *no data is lost*.

Tim Rightnour    -