Veritas-bu

Re: [Veritas-bu] In-File Delta Technology

2009-06-08 14:29:16
Subject: Re: [Veritas-bu] In-File Delta Technology
From: A Darren Dunham <ddunham AT taos DOT com>
To: veritas-bu AT mailman.eng.auburn DOT edu
Date: Mon, 8 Jun 2009 18:26:06 +0000
On Mon, Jun 08, 2009 at 01:18:48PM -0500, Nick Majeran wrote:
>  Most modern OSen should have a capable fs abstraction layer, like VFS,
> which should remove the client from having to know too much about the
> underlying file system, I would assume.

The abstraction layer usually doesn't have enough information to help.
You want to know "what blocks have been modified since timestamp X?" or
you need the ability to create snapshots and get back changed blocks
since that point.  Even if a filesystem has snapshots (like ZFS) doesn't
mean that it will give you that information.  

> Plus, rsync can do it, as long as
> you aren't using the --whole-file option.

Rsync requires access to both copies to do the comparison.  If
everything is on disk, this isn't too bad.  If one side is tape only,
then it's much more difficult.

-- 
Darren
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