From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: Data Deduplication with the help of an online filesystem check Date: Tue, 28 Apr 2009 09:58:22 -0400 Message-ID: <1240927102.15136.0.camel@think.oraclecorp.com> References: <20090427033331.GC17677@cip.informatik.uni-erlangen.de> <1240839448.26451.13.camel@think.oraclecorp.com> <20090428052215.GA22921@cip.informatik.uni-erlangen.de> <1240912971.2149.5.camel@think.oraclecorp.com> <2a31deca0904280649w29d9cca8re9c0abc910ff99@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain Cc: Thomas Glanzmann , linux-btrfs@vger.kernel.org To: Andrey Kuzmin Return-path: In-Reply-To: <2a31deca0904280649w29d9cca8re9c0abc910ff99@mail.gmail.com> List-ID: On Tue, 2009-04-28 at 17:49 +0400, Andrey Kuzmin wrote: > On Tue, Apr 28, 2009 at 2:02 PM, Chris Mason wrote: > > On Tue, 2009-04-28 at 07:22 +0200, Thomas Glanzmann wrote: > >> Hello Chris, > >> > >> > There is a btrfs ioctl to clone individual files, and this could be used > >> > to implement an online dedup. But, since it is happening from userland, > >> > you can't lock out all of the other users of a given file. > >> > >> > So, the dedup application would be responsible for making sure a given > >> > file was not being changed while the dedup scan was running. > >> > >> I see, does that mean that I can not do ,,dedup'' for files that are > >> currently opened by a userland program? > > > > No, but it does mean the dedup done from userland is racey. Picture > > Race disappears if (background) dedupe is run against snapshot(s). > True, but then you're only changing the blocks pointed to by the snapshot. The 'master' copy still points to the unduplicated blocks. -chris