From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from meiko.romanrm.net ([195.154.114.20]:44045 "EHLO meiko.romanrm.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751422AbbACV6i (ORCPT ); Sat, 3 Jan 2015 16:58:38 -0500 Date: Sun, 4 Jan 2015 02:58:35 +0500 From: Roman Mamedov To: Duncan <1i5t5.duncan@cox.net> Cc: linux-btrfs@vger.kernel.org Subject: Re: I need to P. are we almost there yet? Message-ID: <20150104025835.02f0d6b8@natsu> In-Reply-To: References: <54A7D3D1.10508@shiftmail.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Sat, 3 Jan 2015 13:11:57 +0000 (UTC) Duncan <1i5t5.duncan@cox.net> wrote: > > What about using btrfs on top of MD raid? > > The problem with that is data integrity. mdraid doesn't have it. btrfs > does. Most importantly however, you aren't any worse off with Btrfs on top of MD, than with Btrfs on a single device, or with Ext4/XFS/JFS/etc on top of MD. Sure you don't get checksum-based recovery from partial corruption of a RAID, but you do get other features of Btrfs, such as robust snapshot support, ability to online-resize up and down, compression, and actually, checksum verification: even if it won't be able to recover from a corruption, at least it will warn you of it (and you could recover from backups), while other FSes will pass through the corrupted data silently. So until Btrfs multi-device support is feature-complete (and yes that includes performance-wise), running Btrfs in single-device mode on top of MD RAID is arguably the most optimal way to use Btrfs in a RAID setup. (Personally I am running Btrfs on top of 7x2TB MD RAID6, 3x2TB MD RAID5 and 2x2TB MD RAID1). -- With respect, Roman