From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from plane.gmane.org ([80.91.229.3]:54932 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752615Ab3EGXGZ (ORCPT ); Tue, 7 May 2013 19:06:25 -0400 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1UZqxk-0001rd-1f for linux-btrfs@vger.kernel.org; Wed, 08 May 2013 01:06:24 +0200 Received: from dyndsl-178-142-088-157.ewe-ip-backbone.de ([178.142.88.157]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 08 May 2013 01:06:24 +0200 Received: from hurikhan77+btrfs by dyndsl-178-142-088-157.ewe-ip-backbone.de with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 08 May 2013 01:06:24 +0200 To: linux-btrfs@vger.kernel.org From: Kai Krakow Subject: Re: Possible to dedpulicate read-only snapshots for space-efficient backups Date: Wed, 08 May 2013 01:04:38 +0200 Message-ID: <9tdo5a-hde.ln1@hurikhan.ath.cx> References: <64hi5a-9rq.ln1@hurikhan.ath.cx> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Sender: linux-btrfs-owner@vger.kernel.org List-ID: Gabriel de Perthuis schrieb: > It sounds simple, and was sort-of prompted by the new syscall taking > short ranges, but it is tricky figuring out a sane heuristic (when to > hash, when to bail, when to submit without comparing, what should be the > source in the last case), and it's not something I have an immediate > need for. It is also possible to use 9p (with standard cow and/or > small-file dedup) and trade a bit of configuration for much more > space-efficient VMs. > > Finer-grained tracking of which ranges have changed, and maybe some > caching of range hashes, would be a good first step before doing any > crazy large-file heuristics. The hash caching would actually benefit > all use cases. Looking back to good old peer-2-peer days (I think we all got in touch with that the one or the other way), one title pops back into my mind: tiger- tree-hash... I'm not really into it, but would it be possible to use tiger-tree-hashes to find identical blocks? Even accross different sized files... Regards, Kai