Comments: Authenticated sender is <alaric+abwillms AT sdps DOT demon DOT co DOT uk>
From: "Alaric B. Williams" <alaric AT abwillms DOT demon DOT co DOT uk>
To: Lorier <lorier AT ihug DOT co DOT nz>
Date: Sat, 26 Apr 1997 21:45:22 +0000
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Subject: Re: Usage of directory entries
Reply-to: alaric AT abwillms DOT demon DOT co DOT uk
CC: pierre AT tycho DOT com, "Alaric B. Williams" <alaric AT abwillms DOT demon DOT co DOT uk>,
        Matthias DOT Paul AT post DOT rwth-aachen DOT de, opendos-developer AT delorie DOT com
In-reply-to: <m0wL67p-000Fn7C@hn.planet.gen.nz>
Message-ID: <862087322.067830.0@abwillms.demon.co.uk>
Precedence: bulk

On 26 Apr 97 at 23:58, Lorier wrote:

> >You mean /more easily done/. 
 
> Better: You don't have to "lock" files, you don't have race conditions and
> hundres of other problems... There is far more that can go wrong if your
> defragging AND allowing write access... 

One possible solution is to defrag by rebuilding a copy of the file in a linear
region somewhere, then switching from the old copy to the new one. While a file
is being shifted, block read requests come from the old version, and 
block write requests go to the new version, leaving a note to the copier not
to copy the old version of that block from the original contorted file!

The background defrag need not be a perfect defragger. If we can just show that
it will defragment most files without screwing anything up, then we can leave
it chuntering away. A full scale bring-the-system-down defrag tool will only
then be needed if empirical evidence shows that the background one isn't good
enough!

> Adding up a CRC of something that
> changes 1/2 way through is going to make things go BANG I think :)

Now, how would that arise????
 
> > Better for users if it happens invisibly.
 
> Umm... Semi-invisibly :)  Give the "power users" power to do what they NEED. :)

Yes, I'd agree with that. Invisible in general use, but /findable/ if you wanna
see it!

ABW
--
Alaric B. Williams (alaric AT abwillms DOT demon DOT co DOT uk)

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