From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-36-i2.italiaonline.it ([212.48.25.210]:43702 "EHLO libero.it" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751477AbbIQRAM (ORCPT ); Thu, 17 Sep 2015 13:00:12 -0400 Reply-To: kreijack@inwind.it Subject: Re: RAID1 storage server won't boot with one disk missing References: <55FAD9CC.5060206@oracle.com> To: Anand Jain , "erpo41@gmail.com" , linux-btrfs@vger.kernel.org From: Goffredo Baroncelli Message-ID: <55FAF198.2060106@libero.it> Date: Thu, 17 Sep 2015 19:00:08 +0200 MIME-Version: 1.0 In-Reply-To: <55FAD9CC.5060206@oracle.com> Content-Type: text/plain; charset=utf-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: Hi Anand, On 2015-09-17 17:18, Anand Jain wrote: > it looks like -o degraded is going to be a very obvious feature, > I have plans of making it a default feature, and provide -o > nodegraded feature instead. Thanks for comments if any. > > Thanks, Anand I am not sure if there is a "good" default for this kind of problem; there are several aspects: - remote machine: for a remote machine, I think that the root filesystem should be mounted anyway. For a secondary filesystem (home ?), may be that an user intervention could be better (but without home, how an user could log?). - spare: in case of a degraded filesystem, the system could insert a spare disk; or a reshaping could be started (raid5->raid1, raid6->raid5) - initramfs: this is the most complicated things: currently most initramfs don't mount the filesystem if all the volumes aren't available. Allowing a degraded root filesystem means: a) wait for the disks until a timeout b) if the timeout expires, mount in degraded mode (inserting a spare disk if available ?) c) otherwise mount the filesystem as usual - degraded: I think that there are different level of degraded. For example, in case of raid6 a missing device could be acceptable; however in case of a raid5, this should be not allowed; and an user intervention may be preferred. In the past I suggested the use of an helper, mount.btrfs [1], which could handle all these cases better without a kernel intervention: - wait for the devices to appear - verifying if all the needed devices are present - mounting the filesystem passing - all the devices to the kernel (without relying to udev and btrfs dev scan...) - allowing the degraded mode or not (policy) - starting an insertion of the spare (policy) G.Baroncelli [1] http://www.spinics.net/lists/linux-btrfs/msg39706.html -- gpg @keyserver.linux.it: Goffredo Baroncelli Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5