ReadyNAS Pro 516 No Volume Exists

Hi wolfie111 

Your md127 data raid seems to start fine here.

[Thu Apr 21 13:14:22 2022] md/raid:md127: raid level 5 active with 3 out of 3 devices, algorithm 2
[Thu Apr 21 13:14:22 2022] RAID conf printout:
[Thu Apr 21 13:14:22 2022] --- level:5 rd:3 wd:3
[Thu Apr 21 13:14:22 2022] disk 0, o:1, dev:sda4
[Thu Apr 21 13:14:22 2022] disk 1, o:1, dev:sdb4
[Thu Apr 21 13:14:22 2022] disk 2, o:1, dev:sdc4
[Thu Apr 21 13:14:22 2022] md127: detected capacity change from 0 to 4000511819776
[Thu Apr 21 13:14:23 2022] BTRFS: device label 7c6e20ee:data devid 2 transid 797642 /dev/md127

But the filesystem complains that it cannot read the array.

[Thu Apr 21 13:14:24 2022] BTRFS error (device md127): failed to read the system array: -5
[Thu Apr 21 13:14:24 2022] BTRFS error (device md127): open_ctree failed

And the BTRFS log shows that there is a missing raid, beyond md127.

Label: '7c6e20ee:data' uuid: d46a0c6b-9371-4694-8dda-ed1fc2ee239b
Total devices 2 FS bytes used 2.41TiB
devid 2 size 3.64TiB used 414.03GiB path /dev/md127
*** Some devices missing

Looking at the partition table, I see the disks are partitioned into dual partitions of 2TB each (partitions 3 and 4 on each disk).

   8        0 3907018584 sda
   8        1    4194304 sda1
   8        2     524288 sda2
   8        3 1948793912 sda3 <<<<====
   8        4 1953506020 sda4 <<<<====
   8       16 3907018584 sdb
   8       17    4194304 sdb1
   8       18     524288 sdb2
   8       19 1948793912 sdb3 <<<<====
   8       20 1953506020 sdb4 <<<<====
   8       32 3907018584 sdc
   8       33    4194304 sdc1
   8       34     524288 sdc2
   8       35 1948793912 sdc3 <<<<====
   8       36 1953506020 sdc4 <<<<====
   9        0    4192192 md0
   9        1     523264 md1
   9      127 3906749824 md127

That would mean the NAS normally assembles md127 and md126, and the BTRFS filesystem can stick these two raid instances together into one data volume. But I don't see any attempt from the NAS to assemble md126 as one would expected given how the disks are partitioned. But it explains why the BTRFS logs are complaining about a missing raid device.

I don't have a good explanation as to why the NAS isn't attempting to assemble the missing raid. In a case like this, one should examine the raid super blocks to determine what is going on with missing raid. It requires some expertise and Netgear Level 3 support should look at this, realistically. If the data matters, I would suggest to contact then regarding a data recovery contract. It is not easily fixed on your own and certainly goes beyond forum based assistance.

https://kb.netgear.com/69/ReadyNAS-Data-Recovery-Diagnostics-Scope-of-Service 

Cheers