From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f170.google.com ([209.85.212.170]:35258 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753950AbbIHL7X (ORCPT ); Tue, 8 Sep 2015 07:59:23 -0400 Received: by wicge5 with SMTP id ge5so113615643wic.0 for ; Tue, 08 Sep 2015 04:59:22 -0700 (PDT) Received: from [192.168.0.107] (89-212-5-85.static.t-2.net. [89.212.5.85]) by smtp.googlemail.com with ESMTPSA id h8sm4463770wib.21.2015.09.08.04.59.20 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 08 Sep 2015 04:59:20 -0700 (PDT) To: linux-btrfs@vger.kernel.org From: =?UTF-8?Q?Peter_Ke=c5=a1e?= Subject: raid6 + hot spare question Message-ID: <55EECD97.7090109@viidea.com> Date: Tue, 8 Sep 2015 13:59:19 +0200 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: I'm planning to set up a raid6 array with 4 x 4TB drives. Presumably that would result in 8TB of usable space + parity, which is about enough for my data (my data is currently 5TB in raid1, slowly growing at about 1 TB per year, but I often keep some additional backups if space permits). However I'd like to be prepared for a disk failure. Because my server is not easily accessible and disk replacement times can be long, I'm considering the idea of making a 5-drive raid6, thus getting 12TB useable space + parity. In this case, the extra 4TB drive would serve as some sort of a hot spare. My assumption is that if one hard drive fails before the volume is more than 8TB full, I can just rebalance and resize the volume from 12 TB back to 8 TB essentially going from 5-drive raid6 to 4-drive raid6). Can anyone confirm my assumption? Can I indeed rebalance from 5-drive raid6 to 4-drive raid6 if the volume is not too big? Thanks, Peter