ReadyNAS RN10400 DATA DEAD -> Reboot-> remove inactive volumes to use disk

Current status: No files are accesible and when the drive is accessed via the web interface, I get a message:

"Remove inactive volumes to use the disk. Disk #1, 2, 3, 4."

Here is what happened:

Six days ago, I started getting emails from my ReadyNAS with the following message:

"Detected high uncorrectable error count: [2528] on disk 2 (Internal) [ST1000DM003-1ER162, Z4Y5Q3BG]. This condition often indicates an impending failure. Be prepared to replace this disk to maintain data redundancy."

The sector count increased from 2312 to 2528 in a matter of 2 min and I got 18 such emails. I had no idea what this meant so I asked one of my staff to open the software and see what the problem was. When he logged in , he got a message to upgrade firmware which did. System log says : "System: Firmware was upgraded to 6.10.2."

After that, the previos messages stopped but a new message started coming :

"Less than 20% of volume data's capacity is free. Performance on volume data will degrade if additional capacity is consumed. NETGEAR recommends that you add capacity to avoid performance degradation"

This went on for three days where I would periodically get these messages. The a new message started coming since two yesterday : "Volume: Volume data is Degraded". After that the last two messages came once more.

I was worried about the earlier message about the  "impending failure" so I purchased a new 1 TB HDD and last night I swapped out disk #2 with a new one. Log says:  "Disk: Disk Model:ST1000DM010-2EP102 Serial:ZN1DEHF4 was added to Channel 2 of the head unit."

The system then started the resync operation with an estimate time of 16 hours. I checked earlier today and it had reached 50% and was going slower than initial estimate. I had left the system disconnected from the network so that nobody adds new data while the resync was going on.

Just a few hours back when I checked the status on the from LED display, I saw the message : "data DEAD"

I reconnected the network and opened the NAS interface on the browser. And I saw the disk #4 (note: disk #2 was replaced) was showing RED and indicating DEAD status while the other three disks were showing GREEN. I check if the drive was still accessible and it was. But on closer inspection, I saw several folders were missing and some of them were also empty.

I immediately googled the messages and saw a few posts (including this forum) where people had similar issues where a different drive showed up dead after replacing one of the drives and the resync was complete. However those people still had access to all their data and proceeded to back it up whereas my data was already partially missing.

I didn't want to believe that disk #4 failed while the resync operation was happening so I thought maybe this was just some bug (probably a mistake on my part). I though I will try to reboot the system. The system rebooted fine but now I am getting a different message and not able to access the drive at all.

"Remove inactive volumes to use the disk. Disk #1, 2, 3, 4."

However, all four drives are now showing green which I am guessing means the disks are fine.

In the System-> Volume TAB, I see two volumes: one which shows data 2.72 TB ,Free:0) which is compatible with the original volume and a second one which says Data : 0 , Free : 0 (See attached image)

I am clueless on what to do now. Have I lost all my data? Any help would be deeply appreciated.

The unit is about 5.5 years old.

Log messages from past week are given below

Jan 22, 2020 10:24:35 AM System: ReadyNASOS background service started.
Jan 22, 2020 10:20:40 AM System: The system is rebooting.
Jan 22, 2020 03:45:59 AM Volume: Volume data is resynced.
Jan 22, 2020 03:45:38 AM Disk: Disk in channel 4 (Internal) changed state from ONLINE to FAILED.
Jan 22, 2020 03:45:37 AM Disk: Disk in channel 2 (Internal) changed state from RESYNC to ONLINE.
Jan 22, 2020 03:45:36 AM Volume: Volume data health changed from Degraded to Dead.
Jan 22, 2020 01:00:21 AM System: Alert message failed to send.
Jan 22, 2020 01:00:21 AM Volume: Volume data is Degraded.
Jan 21, 2020 12:13:51 PM Volume: Resyncing started for Volume data.
Jan 21, 2020 12:13:27 PM Disk: Disk Model:ST1000DM010-2EP102 Serial:ZN1DEHF4 was added to Channel 2 of the head unit.
Jan 21, 2020 12:04:57 PM Volume: The resync operation finished on volume data. However, the volume is still degraded.
Jan 21, 2020 12:04:45 PM Disk: Disk Model:ST1000DM003-1ER162 Serial:Z4Y5Q3BG was removed from Channel 2 of the head unit.
Jan 21, 2020 11:58:06 AM Volume: Resyncing started for Volume data.
Jan 21, 2020 11:58:03 AM Volume: Volume data is Degraded.
Jan 21, 2020 11:57:52 AM System: ReadyNASOS background service started.
Jan 21, 2020 11:57:46 AM Volume: Less than 20% of volume data's capacity is free. Performance on volume data will degrade if additional capacity is consumed. NETGEAR recommends that you add capacity to avoid performance degradation.
Jan 20, 2020 01:35:36 AM System: The system is shutting down.
Jan 20, 2020 01:08:37 AM Volume: Volume data is Degraded.
Jan 20, 2020 01:08:31 AM System: ReadyNASOS background service started.
Jan 20, 2020 01:08:26 AM Volume: Less than 20% of volume data's capacity is free. Performance on volume data will degrade if additional capacity is consumed. NETGEAR recommends that you add capacity to avoid performance degradation.
Jan 20, 2020 12:41:36 AM System: The system is shutting down.
Jan 20, 2020 12:41:19 AM System: ReadyNASOS background service started.
Jan 20, 2020 12:41:14 AM Volume: Less than 20% of volume data's capacity is free. Performance on volume data will degrade if additional capacity is consumed. NETGEAR recommends that you add capacity to avoid performance degradation.
Jan 19, 2020 09:21:03 PM System: The system is shutting down.
Jan 18, 2020 10:01:37 AM System: ReadyNASOS background service started.
Jan 18, 2020 10:01:33 AM Volume: Less than 20% of volume data's capacity is free. Performance on volume data will degrade if additional capacity is consumed. NETGEAR recommends that you add capacity to avoid performance degradation.
Jan 17, 2020 08:47:32 AM System: The system is shutting down.
Jan 17, 2020 03:13:03 AM System: ReadyNASOS background service started.
Jan 17, 2020 03:12:41 AM System: Antivirus is disabled from 6.10.0 for this device.
Jan 17, 2020 03:12:41 AM System: Firmware was upgraded to 6.10.2.
Jan 17, 2020 03:12:39 AM Volume: Less than 20% of volume data's capacity is free. Performance on volume data will degrade if additional capacity is consumed. NETGEAR recommends that you add capacity to avoid performance degradation.
Jan 17, 2020 02:56:54 AM System: The system is shutting down.