From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from plane.gmane.org ([80.91.229.3]:49322 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751192AbaCYBLx (ORCPT ); Mon, 24 Mar 2014 21:11:53 -0400 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1WSFuC-00059B-Kl for linux-btrfs@vger.kernel.org; Tue, 25 Mar 2014 02:11:52 +0100 Received: from cpc21-stap10-2-0-cust974.12-2.cable.virginm.net ([86.0.163.207]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 25 Mar 2014 02:11:52 +0100 Received: from m_btrfs by cpc21-stap10-2-0-cust974.12-2.cable.virginm.net with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 25 Mar 2014 02:11:52 +0100 To: linux-btrfs@vger.kernel.org From: Martin Subject: Re: Btrfs and raid5 status with kernel 3.14, documentation, and howto Date: Tue, 25 Mar 2014 01:11:43 +0000 Message-ID: References: <20140323225657.GA17039@merlins.org> <20140324215239.GC11533@merlins.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 In-Reply-To: <20140324215239.GC11533@merlins.org> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 24/03/14 21:52, Marc MERLIN wrote: > On Mon, Mar 24, 2014 at 07:17:12PM +0000, Martin wrote: >> Thanks for the very good summary. >> >> So... In very brief summary, btrfs raid5 is very much a work in progress. > > If you know how to use it, which I didn't know do now, it's technically very > usable as is. The corner cases are in having a failing drive which you can't > hot remove because you can't write to it. > It's unfortunate that you can't just "kill" a drive without umounting, > making the drive disappear so that btrfs can't see it (dmsetup remove > cryptname for me, so it's easy to do remotely), and remounting in degraded > mode. Yes, looking good, but for my usage I need the option to run ok with a failed drive. So, that's one to keep a development eye on for continued progress... >> Question: Is the raid5 going to be seamlessly part of the >> error-correcting raids whereby raid5, raid6, >> raid-with-n-redundant-drives are all coded as one configurable raid? > > I'm not sure I parse your question. As far as btrfs is concerned you can > switch from non raid to raid5 to raid6 by adding a drive and rebalancing > which effectively reads and re-writes all the blocks in the new format. There's a big thread a short while ago about using parity across n-devices where the parity is spread such that you can have 1, 2, and up to 6 redundant devices. Well beyond just raid5 and raid6: http://lwn.net/Articles/579034/ >> Also (second question): What happened to the raid naming scheme that >> better described the btrfs-style of raid by explicitly numbering the >> number of devices used for mirroring, striping, and error-correction? > > btrfs fi show kind of tells you that if you know how to read it (I didn't > initially). What's missing for you? btrfs raid1 at present is always just the two copies of data spread across whatever number of disks you have. A more flexible arrangement is to be able to set to have say 3 copies of data and use say 4 disks. There's a new naming scheme proposed somewhere that enumerates all the permutations possible for numbers of devices, copies and parity that btrfs can support. For me, that is a 'killer' feature beyond what can be done with md-raid for example. Regards, Martin