Re: how to backup git

From: Daniel Barkalow <barkalow@iabervon.org>
Date: May 12, 2008, 21:19 UTC
Message-ID: <alpine.LNX.1.00.0805121647540.19665@iabervon.org>
In-Reply-To: <48285087.3090402@gmail.com>

On Mon, 12 May 2008, bill lam wrote:

Show 8 quoted lines

> Johannes Schindelin wrote:
> > > I'd rsync just the .git directory.
> 
> Thanks to all responders for quick reply. I still have a related question. svn
> has a hotcopy command to ensure integrity so that it is possible to backup
> without shutting down the svn server. If someone update the .git while I am
> performing backup using tar or rsync? Will the atomicity of that commit still
> preserve in my backup copy?

There's the risk that the backup will start, it will copy all of the objects, then a git commit happens, which adds more objects (after rsync has passed) and updates a "refs" entry to refer to one of them, and then rsync copies the "refs" directory.

It's likewise possible to have part of the information for a commit copied and part of it not. This commit will be clearly broken, however (one or more objects not found).

So, essentially, every commit goes through the stages of not at all written, partially written but invalid, and valid and correct. Independantly, which commit is the latest is updated atomically. It's possible for an ill-timed backup to get a branch updated to a commit that's not yet valid in the backup. In you restored from this, you'd need to use one of several methods (mainly reflogs) to get back to the last valid commit that got backed up.

On the other hand, git will never, even in this sort of backup, end up with a commit that's valid but not completely correct.

	-Daniel
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