Date: Sun, 21 Feb 2010 19:22:29 +0100 From: Polytropon <freebsd@edvax.de> To: Aiza <aiza21@comclark.com> Cc: freebsd-questions <questions@freebsd.org> Subject: Re: Dump questions Message-ID: <20100221192229.705dfd19.freebsd@edvax.de> In-Reply-To: <4B812C8F.40102@comclark.com> References: <4B80ABBA.9000707@comclark.com> <20100221110358.9ec8b286.freebsd@edvax.de> <4B812C8F.40102@comclark.com>
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On Sun, 21 Feb 2010 20:52:31 +0800, Aiza <aiza21@comclark.com> wrote: > Polytropon wrote: > > On Sun, 21 Feb 2010 11:42:50 +0800, Aiza <aiza21@comclark.com> wrote: > >> 1. Using the -L flag to create a snapshot of the > >> live running file system. > >> > >> Does this mean that a complete copy of the file > >> system is written to .snap directory? > > > > No. The snapshot, quite incorrectly explained, is a saved > > delta between the file system on disk at a given state, to > > fixate further modifications (that are not included in the > > dump, of course). > > > > Sorry, I read your words but have no clue as what you are trying to say > with that statement. As i understand 'delta' to mean, the difference in > file system content between a point in time 'A' and 'B' some point in > time later in the future. Now just what is snapshot recording between > point 'A' and 'B' and how does that apply to what dump is going to read > and write? Oh, I see I did express a bit unclear. The snapshot means that the filesystem's status of a certain point in time - here: when dump is beginning to run - is fixated in a snapshot file, representing its exact content at time A. This representation is subject to the dump. All further deltas after A are not incorporated into the snapshot, and of course not into the dump. This means that all changes after A are lost if the backup is restored. A welcome solution, especially when dumo + restore are used to transfer system and user data, is to first run dump and restore, and then use cpdup to commit changes that took place during or right after the dump to the target. -- Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ...
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