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Date:      Mon, 28 Jan 2002 20:13:15 +0100
From:      Poul-Henning Kamp <phk@critter.freebsd.dk>
To:        "Kenneth D. Merry" <ken@kdm.org>
Cc:        arch@FreeBSD.ORG
Subject:   Re: Geom project, limited preview... 
Message-ID:  <45940.1012245195@critter.freebsd.dk>
In-Reply-To: Your message of "Mon, 28 Jan 2002 11:15:14 MST." <20020128111514.A3819@panzer.kdm.org> 

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In message <20020128111514.A3819@panzer.kdm.org>, "Kenneth D. Merry" writes:

>Looks interesting.
>
>If you end up doing any striping, mirroring or RAID with this, I would
>suggest/request you put hooks in for:
>
> - different on-disk metadata types.  There is a specific project I've been
>   working on (not for FreeBSD, unfortunately) that involves changing a
>   software RAID implementation to have support for multiple types of on-disk
>   metadata.

My plan was to recognize what I can, and have a way for userland to configure
as well.

> - support for external parity engines for RAID-5 parity calculation.  (If
>   you do any sort of RAID-5 with this.)

Well, I have no raid-5 hardware so this would probably have to be left
to somebody else.

>Another interesting thing you could do with this would be tied in with your
>"COW" proposal.  In essence, you could create a block-level checkpoint
>functionality.  You would have the primary device, which would continue to
>receive read and write requests after the checkpoint instantiation, and
>then the secondary device, where you would copy the original version of any
>sectors written to the primary device after the checkpoint.

Hmm, that is the reverse of what I thought it should do, but I can
certainly see the point...

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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