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From: Terry Lambert <terry@lambert.org>
Message-Id: <199610022154.OAA04828@phaeton.artisoft.com>
Subject: Re: VPS mailing list, BSD interest?
To: avalon@coombs.anu.edu.au (Darren Reed)
Date: Wed, 2 Oct 1996 14:54:20 -0700 (MST)
Cc: jrg@demon.net, mrg@eterna.com.au, hackers@freebsd.org,
        tech-kern@netbsd.org
In-Reply-To: <199610021219.FAA02036@freefall.freebsd.org> from "Darren Reed" at Oct 2, 96 10:18:58 pm
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> Hmmm, having used LVM, seen ccd docs, to me, it should be something
> like this:
> 
> +----------------------------------+
> |   FFS/UFS/NTFS/LFS/VXFS/EXT2/... |
> +------------------+---------+-----+
> |                  |  LVM    |     |
> |       disks      +---+-----+ CCD |
> |                      |           |
> |    hd* sd* xd*       +-----------+
> |                                  |
> +----------------------------------+

Ugh.

A FS type must be able to express a preference or deny an underlying
media type.  For instance, FFS should be permitted to prevent you
putting it on a device which has Logical Device Attributes of
LDA_MAY_GROW or LDA_MAY_SHRINK, since handling of these operations
requires that the FS register a callback to allow or veto the
operation, depending on whether or not it has handlers.

Similarly, JFS/NTFS/LFS/etc. which can handle changing agregation
sizes with an LVM facility (adding or deleting PP's from the volume)
must call back to determine allowable size change increment.  I believe
JFS requires a 4M or an 8M increment, in all cases, for instance.

This is a highly complex issue.  I would warn against a soloution
that can be represented as a two dimensional image.  8-(.


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.