OS6 Data Recovery - How to Mount BTRFS Volumes

Thanks for your help on this mgdm.

First, one change from my previous test - I downloaded and clean installed Debian 7.6.0. Default install with the /home directory in a separate partition. This time, after installing mdadm (apt-get install mdadm) and btrfs-tools (apt get install btrfs-tools), it appears to auto assemble the raid array during startup without any other commands.

When I do the command cat /proc/mdstat what I see is the following:

Personalities : [raid6] [raid5] [raid4] [raid1]
md125 : active (auto-read-only) raid1 sdb1[0] sdd1[2] sdc1[1]
4192192 blocks super 1.2 [4/3] [UUU_]

md126 : active (auto-read-only) raid6 sdb2[0] sdd2[2] sdc2[1]
1047936 blocks super 1.2 level 6, 64k chunk, algorithm 2 [4/3] [UUU_]

md127 : active (auto-read-only) raid6 sdb3[0] sdd3[2] sdc3[1]
3897329408 blocks super 1.2 level 6, 64k chunk, algorithm 2 [4/3] [UUU_]

unused devices : <none>

When I do the command btrfs fi label /dev/md127 I get the following:

5e276850:TESTFLX6

The name "TESTFLX6" is the name I gave to the RAID 6 data volume.

When I follow your instructions for mounting the partition, using these commands:

mdadm --assemble --scan
cat /proc/mdstat
mount -t btrfs -o ro /dev/md127 /mnt

I get the following:

mdadm --assemble --scan
(response) mdadm: No arrays found in config file or automatically

cat /proc/mdstat
(response) As shown above

mount -t btrfs -o ro /dev/md127 /mnt
(response) mount: wrong fs type, bad option, bad superblock on /dev/md127, missing codepage or helper program, or other error. In some cases useful info is found in syslog - try dmesg | tail or so

When I put in dmesg | tail I get the following:

[ 1305.427980] device label 5e276850:TESTFLX6 devid 1 transid 34 /dev/md127
[ 1305.428326] btrfs: disk space caching is enabled
[ 1305.428329] BTRFS: couldn't mount because of unsupported optional features (20).
[ 1305.459491] btrfs: open_ctree failed

This is where I'm stuck. Any ideas on troubleshooting this?

Stan