From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from plane.gmane.org ([80.91.229.3]:54177 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751586AbaDKR6d (ORCPT ); Fri, 11 Apr 2014 13:58:33 -0400 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1WYfih-00063T-N6 for linux-btrfs@vger.kernel.org; Fri, 11 Apr 2014 19:58:31 +0200 Received: from ip68-231-22-224.ph.ph.cox.net ([68.231.22.224]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Fri, 11 Apr 2014 19:58:31 +0200 Received: from 1i5t5.duncan by ip68-231-22-224.ph.ph.cox.net with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Fri, 11 Apr 2014 19:58:31 +0200 To: linux-btrfs@vger.kernel.org From: Duncan <1i5t5.duncan@cox.net> Subject: Re: using same btrfs from diferent distros/kernels Date: Fri, 11 Apr 2014 17:58:18 +0000 (UTC) Message-ID: References: <5347FA01.3090809@netvision.com.py> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: Julio E. Gonzalez P. posted on Fri, 11 Apr 2014 10:19:45 -0400 as excerpted: > I have a multiboot PC with Centos 6.5, Fedora 20, and Ubuntu 13.10. Also > there is a btrfs partition I want to mount, read and write from the 3 > diferent distros. > > Is this "safe" ? Is the btrfs versions from this 3 distros compatible > between them ? > This is for testing and learning only. I've no idea what kernels all those distros ship with, but in general, for some time now btrfs on-device format has been guaranteed forward compatibility, but not necessarily backward compatibility (or the reverse, from the kernel's perspective instead of the device's on-disk format, backward compatibility since newer kernels can mount older on- device-formats, but not forward compatibility since older kernels won't necessarily mount newer on-device-formats without error). That is, you can always move to a newer kernel, but if there were changes in on-device format between kernels, once mounted read/write with the newer kernel, you aren't guaranteed that mounting with the older kernel will still be error free. Further, until very recently (kernel v3.13 IIRC), btrfs still being under rather active development and bug-fixing, users are always encouraged to run the latest stable kernel, as it will have fixes for known bugs that affected earlier kernels. So regardless of the distro you run, you want to run a new kernel. That said, with kernel v3.13, the btrfs kconfig option warning was toned down quite a bit, and they're making stronger efforts to backport fixes to stable now. So in theory at least you should be able to run the latest version of any stable-series kernel newer than v3.13 (tho still with the forward compatibility only guarantee). Active stable series before that are likely to get fixes as they are making the backporting effort now, but it's not guaranteed. Of course v3.13 is still relatively new as the newest release is only the v3.14 series, and to my knowledge nobody has yet taken up either v3.13 or v3.14 as a longterm support kernel, so their stable series support is likely to be rather short, but going forward it's still an important turning point, as a year from now the current kernel will be perhaps v3.19, and there's likely to be at least one v3.13+ longer term support kernel available. So bottom line, regardless of what distro(s) you run, you should be good as long as you're running the latest stable kernel series on each. And from v3.13 on, you should be good as long as you're running /any/ currently active stable kernel series v3.13 or newer. But in any case, try to keep your kernels in sync between distros, because there is still that one-way-compatibility-guarantee only. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman