From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans Reiser Subject: Re: COW files Date: Sat, 29 Oct 2005 09:13:23 -0700 Message-ID: <43639FA3.1070204@namesys.com> References: Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com In-Reply-To: List-Id: Content-Type: text/plain; charset="us-ascii" To: Gregory Maxwell Cc: "reiserfs-list@namesys.com" Gregory Maxwell wrote: >Any thought to making a file plugin that creates copy on write files? >The operation would be something like a hardlink which is invisible to >the user and broken as soon as either file is modified. > >Files could be COWed by a flag on the cp command (or really, perhaps >that should be the default behavior) or with a utility (perhaps run as >a periodic script to locate duplicates and COW them. This would >greatly speed up the process of copying files. > >The behavior on break could be to duplicate the whole cowed file on >the first right, or allow a COWed file to have alternate choices for >blocks. Files would remain cowed until decowed, which would likely be >bad for performance (due to fragmentation of alternate versions >causing gaps in sequential scans), so the repacker could be taught to >decow files that have too many alternate blocks. > > > > we are open to patches for this, and nobody is writing one....;-)