From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from plane.gmane.org ([80.91.229.3]:58575 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751680AbcDUFP4 (ORCPT ); Thu, 21 Apr 2016 01:15:56 -0400 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1at6y2-0001oM-31 for linux-btrfs@vger.kernel.org; Thu, 21 Apr 2016 07:15:54 +0200 Received: from p50908ea2.dip0.t-ipconnect.de ([80.144.142.162]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 21 Apr 2016 07:15:54 +0200 Received: from matthias by p50908ea2.dip0.t-ipconnect.de with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 21 Apr 2016 07:15:54 +0200 To: linux-btrfs@vger.kernel.org From: Matthias Bodenbinder Subject: Re: Question: raid1 behaviour on failure Date: Thu, 21 Apr 2016 07:15:48 +0200 Message-ID: References: <57148B2E.6010904@cn.fujitsu.com> <571784DF.3060800@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <571784DF.3060800@oracle.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: Am 20.04.2016 um 15:32 schrieb Anand Jain: >> 1. mount the raid1 (2 disc with different size) > >> 2. unplug the biggest drive (hotplug) > > Btrfs won't know that you have plugged-out a disk. > Though it experiences IO failures, it won't close the bdev. Well, as far as I can tell mdadm can handle this use case. I tested that. I have an mdadm raid5 running. I accidentially unplugged a sata cable from one of the devices and the raid still worked. I did not even notice that the cable was unplugged until a few hours later. Then I plugged in the cable agaib and that was it. mdadm recovered the raid5 without any problem. -> This is redunancy! > >> 3. try to copy something to the degraded raid1 > > This will work as long as you do _not_ run unmount/mount. I did not umount the raid1 when I tried to copy something. As you can see from the sequence of events: I removed the drive and immdiately afterwards tried to copy something to the degraded array. This copy failed with a crash of the btrfs module. -> This is NOT redundancy. The ummount and mount operations are coming afterwards. In a nutshell I have to say that the btrfs behaviour is by no means compliant with my understanding of redundancy. Matthias