OS6 Data Recovery - How to Mount BTRFS Volumes

I tested the mounting procedure detailed in the previous post on the two disks Array grabbed from my ReadyNAS RN102 (assembled with two Toshiba DT01ACA100) which is running ReadyOS 6.1.9 RC8.

I used a Fedora 20 x64 XFCE Live Image not yum updated (it's exactly the 03.07.2014 respin, so quite updated yet) and below my findings:

Software components:

[root@localhost ~]# rpm -q btrfs-progs
btrfs-progs-3.14.2-3.fc20.x86_64

[root@localhost ~]# btrfs version
Btrfs v3.14.2

[root@localhost ~]# uname -ar
Linux localhost 3.14.9-200.fc20.x86_64 #1 SMP Thu Jun 26 21:40:51 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

Connected disks status:

[root@localhost ~]# fdisk -l

Disk /dev/sda: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 328E1A16-CB49-47FA-9421-D9608DCA2752

Device           Start          End   Size Type
/dev/sda1           64      8388671     4G Linux RAID
/dev/sda2      8388672      9437247   512M Linux RAID
/dev/sda3      9437248   1953521072   927G Linux RAID


Disk /dev/sdb: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: B5EEA0F0-F7CD-4E9F-891F-2F1497D59651

Device           Start          End   Size Type
/dev/sdb1           64      8388671     4G Linux RAID
/dev/sdb2      8388672      9437247   512M Linux RAID
/dev/sdb3      9437248   1953521072   927G Linux RAID

Disk /dev/md127: 926.9 GiB, 995236642816 bytes, 1943821568 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

Disk /dev/md126: 4 GiB, 4290772992 bytes, 8380416 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

Disk /dev/md125: 511.4 MiB, 536281088 bytes, 1047424 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

mdadm status (initially my array wasn't degraded, it was and it is in good shape):

[root@localhost ~]# cat /proc/mdstat
Personalities : [raid1] 
md125 : active (auto-read-only) raid1 sdb2[0] sda2[1]
      523712 blocks super 1.2 [2/2] [UU]
      
md126 : active (auto-read-only) raid1 sdb1[0] sda1[1]
      4190208 blocks super 1.2 [2/2] [UU]
      
md127 : active (auto-read-only) raid1 sdb3[0] sda3[1]
      971910784 blocks super 1.2 [2/2] [UU]
      bitmap: 0/8 pages [0KB], 65536KB chunk

unused devices: <none>

BTRFS status:

[root@localhost ~]# btrfs fi label /dev/md127
0e35a911:data

mdadm assemble resulted in this message:

[root@localhost ~]# mdadm --assemble --scan
mdadm: No arrays found in config file or automatically

Mounting /dev/md127 (data partition) looks good:

[root@localhost ~]# mount -t btrfs -o ro /dev/md127 /mnt

And here I am (as you can see my array was and is basically empty):

[root@localhost ~]# df -h|grep md127
/dev/md127           927G  3.1M  925G   1% /mnt

[root@localhost ~]# cd /mnt

[root@localhost mnt]# ls -lah
total 36K
drwxr-xr-x.  1 root   root    124 Jul 28 11:36 .
drwxr-xr-x. 18 root   root   4.0K Jul 30 03:54 ..
drwxrwxrwx.  1 root   root     64 Jul 28 11:04 .apps
drwxrwxrwx+  1 nobody nobody    0 Jul 16 11:43 Backup
drwxrwxrwx+  1 nobody nobody    0 Jul 16 11:43 Documents
drwxr-xr-x.  1     98     98   10 Jul 16 11:04 home
drwxrwxrwx+  1 nobody nobody    0 Jul 16 11:43 Music
drwxrwxrwx+  1 nobody nobody    0 Jul 16 11:43 Pictures
drwxr-xr-x.  1 root   root     36 Jul 28 11:36 .purge
drwxr-xr-x.  1 root   root     68 Jul 28 11:36 ._share
drwxr-xr-x.  1 root   root      0 Jul 16 11:04 .vault
drwxrwxrwx+  1 nobody nobody    0 Jul 16 11:43 Videos

Mount point (I show the /dev/md127 only) status:

[root@localhost ~]# mount -l|grep md127
/dev/md127 on /mnt type btrfs (ro,relatime,seclabel,space_cache) [0e35a911:data]

Few dmseg grep messages about BTRFS and md:

Jul 30 04:03:57 localhost kernel: [  719.673597] BTRFS: device label 0e35a911:data devid 1 transid 76 /dev/md127
Jul 30 04:03:57 localhost kernel: BTRFS: device label 0e35a911:data devid 1 transid 76 /dev/md127
Jul 30 04:03:57 localhost kernel: BTRFS info (device md127): disk space caching is enabled
Jul 30 04:03:57 localhost kernel: [  719.674570] BTRFS info (device md127): disk space caching is enabled

[root@localhost Documents]# dmesg|grep md
[   56.422296] md: bind<sda3>
[   56.432502] md: bind<sdb3>
[   58.602410] md: raid1 personality registered for level 1
[   58.603526] md/raid1:md127: active with 2 out of 2 mirrors
[   58.603650] created bitmap (8 pages) for device md127
[   58.603862] md127: bitmap initialized from disk: read 1 pages, set 0 of 14831 bits
[   58.629099] md127: detected capacity change from 0 to 995236642816
[   58.629884] md: bind<sda1>
[   58.632111] md: bind<sda2>
[   58.640096] md: bind<sdb2>
[   58.643333] md/raid1:md125: active with 2 out of 2 mirrors
[   58.643368] md125: detected capacity change from 0 to 536281088
[   58.653856]  md127: unknown partition table
[   58.669308]  md125: unknown partition table
[   58.678096] md: bind<sdb1>
[   58.680007] md/raid1:md126: active with 2 out of 2 mirrors
[   58.680053] md126: detected capacity change from 0 to 4290772992
[   58.686240]  md126: unknown partition table
[   63.132849] systemd-journald[632]: Received request to flush runtime journal from PID 1
[   73.919360] BTRFS: device label 0e35a911:data devid 1 transid 76 /dev/md127
[   74.285276] Adding 523708k swap on /dev/md125.  Priority:-1 extents:1 across:523708k FS
[  719.673597] BTRFS: device label 0e35a911:data devid 1 transid 76 /dev/md127
[  719.674570] BTRFS info (device md127): disk space caching is enabled
[  719.714024] SELinux: initialized (dev md127, type btrfs), uses xattr

Status of /dev/mdx (x=127, 126 and 125) in detail:

[root@localhost ~]# mdadm --detail /dev/md127
/dev/md127:
        Version : 1.2
  Creation Time : Wed Jul 16 11:03:50 2014
     Raid Level : raid1
     Array Size : 971910784 (926.89 GiB 995.24 GB)
  Used Dev Size : 971910784 (926.89 GiB 995.24 GB)
   Raid Devices : 2
  Total Devices : 2
    Persistence : Superblock is persistent

  Intent Bitmap : Internal

    Update Time : Wed Jul 30 04:02:48 2014
          State : active
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           Name : 0e35a911:data-0
           UUID : 1617bc13:e5576688:64018e5b:0ca61008
         Events : 1759

    Number   Major   Minor   RaidDevice State
       0       8       19        0      active sync   /dev/sdb3
       1       8        3        1      active sync   /dev/sda3
[root@localhost ~]# mdadm --detail /dev/md126
/dev/md126:
        Version : 1.2
  Creation Time : Wed Jul 16 11:03:50 2014
     Raid Level : raid1
     Array Size : 4190208 (4.00 GiB 4.29 GB)
  Used Dev Size : 4190208 (4.00 GiB 4.29 GB)
   Raid Devices : 2
  Total Devices : 2
    Persistence : Superblock is persistent

    Update Time : Mon Jul 28 11:46:35 2014
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           Name : 0e35a911:0
           UUID : 7062aefd:dcbae9c7:1dd84684:e7744d65
         Events : 23

    Number   Major   Minor   RaidDevice State
       0       8       17        0      active sync   /dev/sdb1
       1       8        1        1      active sync   /dev/sda1
[root@localhost ~]# mdadm --detail /dev/md125
/dev/md125:
        Version : 1.2
  Creation Time : Wed Jul 16 11:03:50 2014
     Raid Level : raid1
     Array Size : 523712 (511.52 MiB 536.28 MB)
  Used Dev Size : 523712 (511.52 MiB 536.28 MB)
   Raid Devices : 2
  Total Devices : 2
    Persistence : Superblock is persistent

    Update Time : Mon Jul 21 10:11:11 2014
          State : clean
 Active Devices : 2
Working Devices : 2
 Failed Devices : 0
  Spare Devices : 0

           Name : 0e35a911:1
           UUID : 767a9300:bd522aac:366459ee:712f6896
         Events : 19

    Number   Major   Minor   RaidDevice State
       0       8       18        0      active sync   /dev/sdb2
       1       8        2        1      active sync   /dev/sda2

After trying I'm now quite confident about BTRFS data recovery option using an (updated) Linux box: the only test we should do now could be to test a degraded array.