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Forum Discussion
RN626X: Data array missing from mdstat after OS reinstall (password recovery)
Hi all,
Hoping someone can help me safely recover my data array. Details below:
MODEL: ReadyNAS RN626X, 6 disks, RAID 5, ~18TB data (OS 6)
TIMELINE:
1. Admin password stopped working unexpectedly.
2. I pressed the physical reset button on the back of the unit (short press). This did not fix the password, but it did reset the network settings to DHCP (IP address changed).
3. To recover the admin password, I performed a proper OS reinstall via the boot menu (Reset + Power, held until boot menu appeared, selected "OS reinstall"). This successfully reset admin/password to defaults and I could log into the web interface again.
4. However, after logging in:
- System > Volumes shows "data-0" as Healthy (green), RAID 5, Data 18.17TB, Free 0 — looks intact.
- There's also a second entry called "data" (blue), 0TB, RAID unknown — assume this is a fresh empty placeholder from the reinstall.
- System > Shares shows a warning: "No volume exists. Navigate to System -> Volumes page to create a volume."
5. I have NOT clicked "create a volume" or removed any disks, since I'm worried this could format/wipe the existing array.
6. Tried a normal system reboot (not another OS reinstall) — same result persists.
DOWNLOADED LOGS — mdstat.log shows only two arrays:
md0 : active raid1 (6 disks) — 4GB, this looks like the OS partition
md1 : active raid10 (6 disks) — ~1.5GB, created Jul 10 2026, likely a system/swap partition
There is NO third array shown for the actual ~18TB data volume. All 6 disks show as active/clean in both md0 and md1, so I don't believe there's a hardware/disk failure — it looks like the data array simply isn't currently assembled after the OS reinstall.
QUESTION: Is it safe to manually reassemble the missing data array via mdadm/SSH, and if so, could someone walk me through the correct approach for OS 6 (BTRFS-based) so I don't make things worse? I have not attempted any commands yet — waiting for guidance before touching anything.
Happy to post the full mdstat.log output, disk info, or other log files on request.
Thanks in advance for any help!
2 Replies
What you are seeing is the inability of the OS to combine two RAID segments into one. Each of the "volumes" you see is a fragment of /data. Since there cannot be two volumes named /data, it names one after the MDADM RAID on which it resides, data-0. This is probably not an artifact of the re-install. It is most likely an additional effect of the corruption that made your password not work. DO NOT delete either, or you data will become unrecoverable.
The best choice is to simply factory default and restore data from backup. If you have no backup, manual re-assembly is the only other choice. If you have a place for them, you could image the drives as a precaution. There is recovery software out there that can do the hard work for you, but StephenB can help guide you if you want to just do it with native Linux tools.
Even if you successfully recover the volume, it's content is going to be suspect and I would not trust it to stay intact. It may even automatically change to read-only if the corruption warrants. So you will need to back up the contents, factory default, and restore the data as a final step -- ideally before you have written anything new to it. While that's going to be expensive if you don't already have the means to do a backup, especially with the current price of hard drives, it is a start to having the backup you should already have. You may want to consider using a newer NAS for that so you can move away from the unsupported ReadyNAS as your primary storage and relegate it to backup.
QUESTION: Is it safe to manually reassemble the missing data array via mdadm/SSH,
There is always some risk, but often that is small. Download the full log zip file, so you can see more details. If you need help analyzing, then you can upload the full zip to cloud storage, and PM me link (using the envelope icon in the upper right of the forum page). Make sure the permissions allow anyone with the link to download.
md0 : active raid1 (6 disks) — 4GB, this looks like the OS partition
md1 : active raid10 (6 disks) — ~1.5GB, created Jul 10 2026, likely a system/swap partitionYes. md0 is the OS, and md1 is swap.
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