From owner-freebsd-hackers  Wed Oct  2 06:57:39 1996
Return-Path: owner-hackers
Received: (from root@localhost)
          by freefall.freebsd.org (8.7.5/8.7.3) id GAA09033
          for hackers-outgoing; Wed, 2 Oct 1996 06:57:39 -0700 (PDT)
Received: from brasil.moneng.mei.com (brasil.moneng.mei.com [151.186.109.160])
          by freefall.freebsd.org (8.7.5/8.7.3) with ESMTP id GAA09025
          for <hackers@freebsd.org>; Wed, 2 Oct 1996 06:57:36 -0700 (PDT)
Received: (from jgreco@localhost) by brasil.moneng.mei.com (8.7.Beta.1/8.7.Beta.1) id IAA05107; Wed, 2 Oct 1996 08:55:28 -0500
From: Joe Greco <jgreco@brasil.moneng.mei.com>
Message-Id: <199610021355.IAA05107@brasil.moneng.mei.com>
Subject: Re: VPS mailing list, BSD interest?
To: mrg@eterna.com.au (matthew green)
Date: Wed, 2 Oct 1996 08:55:28 -0500 (CDT)
Cc: kpneal@pobox.com, gibbs@freefall.freebsd.org, thorpej@nas.nasa.gov,
        phk@critter.tfs.com, greywolf@siva.captech.com, hackers@freebsd.org,
        tech-kern@netbsd.org, buhrow@cats.ucsc.edu
In-Reply-To: <199610020544.PAA18948@eterna.com.au> from "matthew green" at Oct 2, 96 03:44:14 pm
X-Mailer: ELM [version 2.4 PL24]
Content-Type: text
Sender: owner-hackers@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk

> i like parts of ODS:  it keeps state in dedicated partitions on the
> disk, a metadevice db "replica".  you create several of these partitions
> on your disks and it uses them to keep state -- each one is independant
> or the others.

This works pretty well.

> i also like the model of ODS (as under solaris 2):
> 	- a metadevice acts like a normal disk partition
> 	- a metadevice can be composed of any number of real partitions
> 	  or metadevices, either concatenated or striped, or mirrored.
> 
> you create a mirrored stripe by creating two (or three -- ODS has an,
> IMO, stpuid limit) stripes and then mirroring these two metadevices.
> 
> recent ODS versions include raid5 support, file system extensions, etc.
> 
> i'm fairly conversant in ODS if anyone has other questions.

ODS has (IMHO) a disadvantage...  each metadevice is only allowed to
be a partition.  CCD allows you to stick a disklabel on its "metadevice"
and you can have partition_s_.  This is maybe marginally useful, but I
happen to like it.  It allows me to build an I/O "policy" where I stripe
two drives together and simply consider the aggregate to be a faster
drive... and then I partition it up.

It requires less complexity in ccd.conf.

*shrug*

But..  if I could have something with all the features of ODS under *BSD..
and none of the slowdowns... I would in a minute.

... JG