From mboxrd@z Thu Jan  1 00:00:00 1970
From: Josef Bacik <josef@redhat.com>
Subject: Re: raid1
Date: Mon, 11 Jul 2011 20:38:40 -0400
Message-ID: <4E1B9790.3050002@redhat.com>
References: <CAJ1PRSkz86G+4XfDMp1fq8f7ar5LOPux06FJTQ4WxhkT1Bu6vQ@mail.gmail.com>
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Cc: linux-btrfs@vger.kernel.org
To: "krzf83@gmail.com" <krzf83@gmail.com>
Return-path: <linux-btrfs-owner@vger.kernel.org>
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On 07/11/2011 08:22 PM, krzf83@gmail.com wrote:
> I wanted to confirm that btrfs will continue to work on raid1 when one
> of devices will be gone.
>
> dd if=/dev/null of=img0 bs=1 seek=2G
> dd if=/dev/null of=img1 bs=1 seek=2G
> mkfs.btrfs -d raid1 -m raid1 img0 img1
> losetup /dev/loop1 img0
> losetup /dev/loop2 img1
> mkdir dir
> mount -t btrfs /dev/loop1 dir
> btrfs device scan
> mount -t btrfs /dev/loop1 dir
> echo abc>  dir/a.txt
> umount dir
> losetup -d /dev/loop2
> btrfs device scan
> mount -t btrfs /dev/loop1 dir
> mount: wrong fs type, bad option, bad superblock on /dev/loop1,
>         missing codepage or other error
>         In some cases useful info is found in syslog - try
>         dmesg | tail  or so
>
> am I missing some nuance?

Yeah you need to mount -o degraded.  Thanks,

Josef