Problems accessing gpt raid partitions on linux ubuntu 16.04.2 LTS

I had a 6 year old server which I replaced the hard drives and upgraded last summer. It was a 2 cpu (18 cores each) AMD Athlon system who's only purpose was to run VM's (using kvm)for my grad students to use for testing their research. It contained a 1TB boot disk and 4 - 2T disks in a Raid6 array. Periodically I would take the VM's down and back up the virtual drives. The server was located in a secure server room with limited access. However, earlier this week, the unthinkable happened, and there was a fire in the server room. I was able to access the system remotely and do an orderly shutdown (shutdown -h now).

The machine itself is not too badly damaged, but is full of toxic soot. The techs were able to remove the drives from the machine and clean them. I currently have them in a borrowed desktop 7 core intel machine, and while there are not enough drive bays, there are enough sata ports. The thought was to boot off the transplanted boot disk and mdadm would reassemble the drives based on UUIDs. We could then back up the virtual disks in a priority order. However when we booted, the raid array was not present. Placing them back in the previous machine is not really an option as there is still a significant amount of very fine toxic soot in the case which the fans will spread all over the place.

I'm currently in the process of imaging the raw data from the 4 raid disks to a large external drive using dd so that if they fail because of damage we still have the data. So far the disks are behaving themselves. Two disks have been copied without any errors reported by dd, and the 3rd is underway. There don't seem to be any disk errors reported in the system logs either.

Right now the problem appears to be that the system is not seeing the partitions on the 2TB drives. The command 'parted /dev/sdb print' does not report anything on the drive. I used fdisk and got the following results. I've shown the help menus (but elided to only show the options I used).

Script started on Sat 31 Aug 2019 11:17:57 AM EDT
root@perseus:~/usb2# fsdisk /dev/sdb
Welcome to fdisk (util-linux 2.27.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Command (m for help): p
Disk /dev/sdb: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 2947A17A-DC83-4C60-8D2A-63D2403015DD

Command (m for help): m

Help:
...
  Misc
   m   print this menu
   x   extra functionality (experts only)
...

Command (m for help): x

Expert command (m for help): m

Help (expert commands): m
...
  GPT
   i   change disk GUID
   n   change partition name
   u   change partition UUID
   M   enter protective/hybrid MBR
..

Expert command (m for help): p
Disk /dev/sdb: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 2947A17A-DC83-4C60-8D2A-63D2403015DD
First LBA: 34
Last LBA: 3907029134
Alternative LBA: 3907029167
Partition entries LBA: 2
Allocated partition entries: 128

Expert command (m for help): M
Entering protective/hybrid MBR disklabel.

Expert command (m for help): p
Disk /dev/sdb: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device     Boot Start        End    Sectors Id Type Start-C/H/S   End-C/H/S Attrs
/dev/sdb1           1 3907029167 3907029167 ee GPT        0/2/0 1023/63/255      

Partition 1 does not start on physical sector boundary.

Expert command (m for help): q

root@perseus:~/usb2# exit
exit

Script done on Sat 31 Aug 2019 11:18:51 AM EDT

All of the drives print identical results. I assume that if there was problem during shutdown during the fire, they would not all be corrupted in the same way.

So the partition appears to be there, but parted and partprobe don't find it. I've checked with asmod, and the modules raid456, raid6_pq and async_raid6_recov modules are loaded. As far as I know, if the partition is not in /dev then the variants of mdadm to scan or specifically assemble the raid are not going to work. I did give them a try anyways, but no luck.

The system was reinstalled and configured using the ubuntu 16.04 server installation DVD last summer (the previous raids disks were backed up and replaced with new ones). There was nothing special about the installation, as far as I know, other than using a bridge network device so that the graduate students could access their individual vm's remotely. The boot volume and the raid array were created and configured by the ubuntu installer with default options as far as I remember.

I was trying to follow the advice the following link, but I haven't used anything from it that might be destructive as I'm still in the process of backing up the raw data from the drives.

Partition Not Showing up in /dev

Any ideas how I can make the partitions visible? The grad student is in the process of thesis writing, and while she has most of the data (from previous backups), there is data on these disks that is needed.

Thanks.