linux-kernel - Re: Finding hardlinks

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Date:	Thu, 11 Jan 2007 10:07:13 +0000
From:	Pádraig Brady <P@...igBrady.com>
To:	Frank van Maarseveen <frankvm@...nkvm.com>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Miklos Szeredi <miklos@...redi.hu>, pavel@....cz,
	mikulas@...ax.karlin.mff.cuni.cz, matthew@....cx,
	bhalevy@...asas.com, arjan@...radead.org, jaharkes@...cmu.edu,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	nfsv4@...f.org
Subject: Re: Finding hardlinks

Frank van Maarseveen wrote:
> On Tue, Jan 09, 2007 at 11:26:25AM -0500, Steven Rostedt wrote:
>> On Mon, 2007-01-08 at 13:00 +0100, Miklos Szeredi wrote:
>>
>>>> 50% probability of false positive on 4G files seems like very ugly
>>>> design problem to me.
>>> 4 billion files, each with more than one link is pretty far fetched.
>>> And anyway, filesystems can take steps to prevent collisions, as they
>>> do currently for 32bit st_ino, without serious difficulties
>>> apparently.
>> Maybe not 4 billion files, but you can get a large number of >1 linked
>> files, when you copy full directories with "cp -rl".
> 
> Yes but "cp -rl" is typically done by _developers_ and they tend to
> have a better understanding of this (uh, at least within linux context
> I hope so).

I'm not really following this thread, but that's wrong.
A lot of people use hardlinks to provide snapshot functionality.
I.E. the following can be used to efficiently make snapshots:

rsync /src/ /backup/today
cp -al /backup/today /backup/$Date

See also:

http://www.dirvish.org/
http://www.rsnapshot.org/
http://igmus.org/code/

> Also, just adding hard-links doesn't increase the number of inodes.

I don't think that was the point.

Pádraig.
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