NV+ v2 failed 3 disks at once and went life support

Event diary: 3 March 2021  ~16:30 United Kingdom Time (started typing those notes few hours later)

I have a NV+v2 (4x 3TB) which I recently put back online, after replacing  (8 January 2021) HDD2 which was a “Seagate refurb under warranty”.

I also have two RN214; all my NASes stop once a week for 1h: NAS#2 (NV+v2) stops on Monday morning between 2 & 3am, Nas#3 (RN214) between 3 & 4am, Nas#4 (214) between 4 & 5am.

Sunday 21 Feb, HD4 on the NV+ flagged some error, (64), and I was keeping an eye on it; the following Sunday (when I checked), no further errors had been detected.

Today, (3 March) I wanted to do some configuring on the other NASes, and I looked at the NV+ too, but although RaidAir saw it fine, I could not get the admin page up. I looked at the front of the NAS (all NASses are under the desk) and I saw:

LEDs:    HD 2, 3, 4 were flashing

Screen:  HD 2, 3, 4 faulty, Volume C is DEAD.

I powered it off, but although it said "Powering off  GoodBye ...", nothing happened for 5 minutes. NV+ seemed to respond to the power button when pressed again after some time, but again, nothing happened, so, after 4 minutes, I unplugged it from the back.

On restart, all the 4HD LED came up solid. The screen displayed:

Checking FS

Testing Disk 1

Resynching

C Unprotected

Vol C Life Supp !!

Admin page was up, but when I tried to download the log files, NOTHING happened.

I had a look at the content with the File manager: two directories seemed to have data, but the files did not seem to open

The others directories are empty. Existing data was ~4TB.

I switched the NAS off, took all the disks out and tested them. Disk 4 is faulty (as expected), Disk 1, 2 (six weeks old) & 3 passed Quick and Extended tests with WD DLGDIAG (and Victoria). The NAS has been “off” ever since (unplugged), not sure if I can access the logs when diskless.

Is there any way I can reinsert the disks, revert that incorrect synch and return to an “unprotected” array of 3 healthy disks?

Many Thanks in advance, Berillio

Further details:

1) the NV+ v2 is diskless and switched off, while the HD testing was carried out;

2) the only logs I have date 8 january 2021, post the resinch which took place after replacing the HD in slot 2;

3) two days after the failure yahoo delivered a string of ~30 mails which were not in the inbox when I started writing these notes: further HD4 errors (from the original 64, detected on 21 February) were being detected from Sunday 28 February 19:08;

4) this NV+ v2 had a similar issue in November 2014 (case # 24263236); going back one firmware version ‘somewhat’ gave me back access to the  “unprotected” disk array. The NV+ was then phased out, replaced by a RN104, which failed in 2018, but its entire array went into a RN 214 without loss of data, while a 2nd RN214 was bought at the same time to cover the data needs; the NV+ was brought back in April 2020 as I needed space for data, but it was seldom accessed, it was just a file repository; I was aware that one disk (HDD2) may be weak, so I wasn’t surprised when it failed in January 2021.

I attach the only availlable logs and the email history for the relative events

uh? I cannot attach the logs, zip is not at allowed extension? how do I do that?