From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f49.google.com ([209.85.215.49]:35337 "EHLO mail-lf0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752133AbdIKD30 (ORCPT ); Sun, 10 Sep 2017 23:29:26 -0400 Received: by mail-lf0-f49.google.com with SMTP id d17so15310131lfe.2 for ; Sun, 10 Sep 2017 20:29:25 -0700 (PDT) Subject: Re: Help me understand what is going on with my RAID1 FS To: Dmitrii Tcvetkov Cc: FLJ , linux-btrfs@vger.kernel.org References: <1F3219B0-72B2-4201-8C96-E6FBFD02A413@demfloro.ru> <20170910231727.65bbb2aa@demfloro.ru> From: Andrei Borzenkov Message-ID: Date: Mon, 11 Sep 2017 06:29:20 +0300 MIME-Version: 1.0 In-Reply-To: <20170910231727.65bbb2aa@demfloro.ru> Content-Type: text/plain; charset=utf-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: 10.09.2017 23:17, Dmitrii Tcvetkov пишет: >>> Drive1 Drive2 Drive3 >>> X X >>> X X >>> X X >>> >>> Where X is a chunk of raid1 block group. >> >> But this table clearly shows that adding third drive increases free >> space by 50%. You need to reallocate data to actually make use of it, >> but it was done in this case. > > It increases it but I don't see how this space is in any way useful > unless data is in single profile. After full balance chunks will be > spread over 3 devices, how it helps in raid1 data profile case? > A1 A2 => A1 A2 - => A1 A2 B1 => A1 A2 B1 B1 B2 B1 B2 - - B2 - C1 B2 C2 It is raid1 profile on three disks fully utilizing them (assuming equal sizes of course). Where "raid1" means - each data block has two copies on different devices.