Disk 2 has an OS partition but no data partition. Data is mirrored there none the less.
It sounds like you must have RAID-1, but that could be either xraid or flexraid. What tool did you use to extract the data on the PC? With xraid, I suggest linux reader ( http://www.diskinternals.com/linux-reader/ )
When you can access via ssh, did you check OS partition fullness?
df . -h
df . -i
Note you can also remove disk 2 and boot the NAS w/o it. Then it can't sync. It might still lock up.
Be careful not to insert a disk with the NAS running right now though - it will format it, and that is not what you want.
Your OS partition is fine. You must be using xraid, because linux reader wouldn't see the files if you were using flexraid.
I think you have a corrupt file system (and that the lockup is in fsck, not raid resync). Though I can't rule out a failing disk.
You could shut down, and insert disk 2 alone (in the second slot) and see if you get the same behavior. My guess is that you will, but it is worth a try.
It is also worth testing the disks with vendor diags in a PC (seatools for seagate, lifeguard for western digital).
Assuming the lockup happens with only disk 2 installed, the options are to
(a) attempt to repair the file system yourself
(b) contract with Netgear for data recovery
(c) accept the data loss - do a factory reset on the NAS, reconfigure it, and restore the data from a backup.
No matter what option you pick, create a backup on your PC first - using linux reader (copying the files linux reader sees to a USB disk or an NTFS internal disk).
Will try to backup to external disks from NAS during later tonight.
Great. That simplifies the next steps (and you should have all your data).
The fastest way to back up your data is to attach the external disk to your PC and back up over a wired ethernet network. That is a lot faster than attaching the USB drives directly to the NAS. I like to use robocopy or teracopy, and not windows drag and drop. Teracopy has a verify option, which is probably worth using (though it will take longer).
Once that is done, install the replacement disk for disk 1. I like to test it with vendor diags in a PC first. Don't format it- just hot-insert it into the NAS unformatted. Keep in mind that your duo has a size limit of 2 TB or less. I recommend WDC Red drives (wd20efrx or wd10efrx). If you prefer seagate, use a drive from their VN line (not a DM drive).
The compatibility list for the duo is stale, so it isn't very useful anymore.
Obviously one lesson here is that RAID isn't enough to keep your data safe, so you should set yourself a regular backup schedule once everything is running again.
Everything is now up and operational, a new disk1 (WD Red 2T). Backup schedule in place etc. I will also replace disk2 with a fresh WD Red just in case.
I would be very interessted in knowing the root cause to my problem. There are no traces in any of the logs that give any clues. Why is the NAS so sensible to problems during the checking of the filesystem? It doesn't seem like a robust system if problem with one disk makes the whole system freeze!
Since I have grown out of the current system I will also start looking for a replacement NAS.
You could PM mdgm, and ask if he is willing to go through your logs. His signature includes the procedure to get them to Netgear (which is emailing them).
Different disk can fail in different ways. In some cases a failing disk may lead to freezing. Without seeing your logs it seems that is what happened here.
