From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1040.oracle.com ([141.146.126.69]:37896 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754588AbbKMKVr (ORCPT ); Fri, 13 Nov 2015 05:21:47 -0500 Message-ID: <5645B986.9090903@oracle.com> Date: Fri, 13 Nov 2015 18:20:54 +0800 From: Anand Jain MIME-Version: 1.0 To: Qu Wenruo , Austin S Hemmelgarn , linux-btrfs@vger.kernel.org Subject: Re: [PATCH 00/15] btrfs: Hot spare and Auto replace References: <1447066589-3835-1-git-send-email-anand.jain@oracle.com> <5643F62D.6050703@cn.fujitsu.com> <56448E58.3070000@gmail.com> <564537D8.5020407@cn.fujitsu.com> In-Reply-To: <564537D8.5020407@cn.fujitsu.com> Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: Thanks for commenting. >>> I'm sorry but I didn't quite see the benefit of a spare device. >> Aside from what Duncan said (and I happen to agree with him), there is >> also the fact that hot-spares are (at least traditionally in most RAID >> systems) usually used with RAID5 or RAID6 (or some other parity scheme). >> >> So, to summarize: >> 1. Hot spares are more useful for most users in global context, and in >> that case only if they have more than one filesystem. >> 2. A pool of hot spares is even more useful. > > Agreed, just as Ducan said. > Although only one spare device is supported yet. You can add more than one spare device currently. >> 3. Assuming whole disk usage (as opposed to partitioning), the hot spare >> will have no load on it until it gets used, at which point it will >> almost always be in better physical condition than the device it >> replaced (which is important for HA systems, in such cases you replace >> the disk that failed, and make the new disk a hot spare) > > OK, that's also right, if no one is calling btrfs dev scan with a interval. Not too sure what you mean about the scan part. Thanks, Anand