From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f180.google.com ([209.85.223.180]:36558 "EHLO mail-io0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752707AbcHOL5k (ORCPT ); Mon, 15 Aug 2016 07:57:40 -0400 Received: by mail-io0-f180.google.com with SMTP id b62so77441519iod.3 for ; Mon, 15 Aug 2016 04:57:40 -0700 (PDT) Subject: Re: About minimal device number for RAID5/6 To: Qu Wenruo , btrfs References: From: "Austin S. Hemmelgarn" Message-ID: Date: Mon, 15 Aug 2016 07:57:17 -0400 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 2016-08-15 03:50, Qu Wenruo wrote: > Hi, > > Recently I found that manpage of mkfs is saying minimal device number > for RAID5 and RAID6 is 2 and 3. > > Personally speaking, although I understand that RAID5/6 only requires > 1/2 devices for parity stripe, it is still quite strange behavior. > > Under most case, user use raid5/6 for striping AND parity. For 2 devices > RAID5, it's just a more expensive RAID1. > > IMHO it's better to warn user about 2 devices RAID5 or 3 devices RAID6. > > Any comment is welcomed. > Based on looking at the code, we do in fact support 2/3 devices for raid5/6 respectively. Personally, I agree that we should warn when trying to do this, but I absolutely don't think we should stop it from happening.