Andi Drebes wrote:
Hi!
I recently tried to mount a filesystem in RAID1 mode using loopback devices. I followed the instructions at [1]. Here's exactly what I've done:
$ dd if=/dev/zero of=raid1_0.img bs=1M count=500
$ dd if=/dev/zero of=raid1_1.img bs=1M count=500
$ mkfs.btrfs -m raid1 -d raid1 raid1_0.img raid1_1.img
$ losetup /dev/loop0 raid1_0.img
$ losetup /dev/loop1 raid1_1.img
$ mount -t btrfs /dev/loop0 /mnt/btrfs
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so
The problem is btrfs randomly changes the "current master"
superblock of the filesystem. Only 1 of the devices will
be mountable. You just have to try the other ones, like:
> $ mount -t btrfs /dev/loop0 /mnt/btrfs
> mount: wrong fs type, bad option, bad superblock on /dev/loop0,
$ mount -t btrfs /dev/loop1 /mnt/btrfs
until you find one that works. I've been testing 4 devices
and often have to try all 4. Maybe someday we will fix this
so ANY raid member can start the mount (but this may need
a disk format change).
jim
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