From mboxrd@z Thu Jan 1 00:00:00 1970 From: jim owens Subject: Re: New feature Idea Date: Wed, 13 Aug 2008 15:28:39 -0400 Message-ID: <48A335E7.4020407@hp.com> References: <48A320A0.80609@gmail.com> <48A32DDE.8070203@hp.com> <48A330A2.6020306@gentoo.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linux-btrfs@vger.kernel.org To: Joe Peterson , Morey Roof Return-path: In-Reply-To: <48A330A2.6020306@gentoo.org> List-ID: Joe Peterson wrote: > My thoughts on what you are saying is that it is not generally a good > idea to assume any filesystem will lay things out in any specific way, > including whether it has one-to-one mapping of files to blocks. In > other words, making a copy of a file on the same filesystem for safety > reasons (unless you are modifying a file and want a backup of its old > state, like emacs' ~ files) is probably not a great habit to get into. > > The implementation details of how a filesystem makes things safer should > be behind-the-scenes (like checksums, multiple-copies-by-default, > mirroring, etc.). That way, you can simply rely on the filesystem to > manage protection of your data rather than going to the effort of > managing multiple copies of files yourself for that reason. I'm a filesystem guy so I only use ones I know do what I want, I never trust ones I don't know about :) I agree with you about the danger of assuming what a filesystem will or won't do on local copies. I also fear that 99% of normal users have an expectation that making a copy makes a new physical instance (which of course is not safe if the device crashes either). I hate dealing with customers that have lost their data because of the filesystem. Morey Roof wrote: > I was hoping to have it specified as a set of mount options or defaults > controlled in the super block so that if you want to use it you can > otherwise it doesn't exist. I don't have veto power in btrfs so my aversion means nothing. As you say, there are a number of good ways to control it. If you pursue this, I might suggest having a dedup limit so they can say "keep at least 2 copies" or "just one". jim