Both disks have the same UUID:
Apr 11 21:47:50 NASBackup kernel: XFS (md8): Filesystem has duplicate UUID 6e5537c6-38fe-4f06-8d46-587f6c2185fe - can't mount
Likely one was rebuilt for the other at some point in the past, so it will only mount the first one, you can change the UUID in either one:
xfs_admin -U generate /dev/sdX1
Note the 1 in the end.
Disk dropped offline, it's on a Marvell controller and these are know to drop disks in some cases, disk4 is on the same controller, has it been there for long and without issues?
Single error is not a problem, but since it happen on all disks you might get more, and that would mean there's trouble, I would say 4 bad SATA cables it's not likely, so maybe controller or if they share some kind of enclosure.
Like I said never had a single duplicate file, and I have over 300TB of data on unRAID servers, to know what you're doing wrong we'd need more details on how and where you end up with duplicates.
What do you mean caused by unRAID? I use unRAID for over 10 years and never had any dupe issues, nor do I remember reading on the forums about anything other than user error regarding dupes.
These usually work well:
Tunable (md_num_stripes): 4096
Tunable (md_sync_window): 2048
Tunable (md_sync_thresh): 2000
If you're sig is correct and you're still using the SAS2LP also change this one:
Tunable (nr_requests): 8
Happened several times to me, since Terminal was included, this one is from v6.5.0, at some point Terminal crashes and stops working, only reboot fixes it.
I believe these are from when it stopped working:
Mar 17 18:54:19 Tower1 nginx: 2018/03/17 18:54:19 [error] 5672#5672: *698426 recv() failed (104: Connection reset by peer) while proxying upgraded connection, client: 192.168.1.130, server: , request: "GET /webterminal/ws HTTP/1.1", upstream: "http://unix:/var/run/ttyd.sock:/ws", host: "1ad7a6e4386dab50134fcb40b4490f1f43e4ce85.unraid.net"
Mar 17 18:54:24 Tower1 unassigned.devices: Device '/dev/sdh1' script file not found. 'REMOVE' script not executed.
Mar 17 18:54:24 Tower1 unassigned.devices: Unmounting disk 'WDC_WD20SPZX-22CRAT0_WD-WXA1E171A1KU'...
Mar 17 18:54:24 Tower1 unassigned.devices: Unmounting '/dev/sdh1'...
Mar 17 18:54:26 Tower1 unassigned.devices: Successfully unmounted '/dev/sdh1'
Mar 17 18:54:26 Tower1 unassigned.devices: Disk with serial 'WDC_WD20SPZX-22CRAT0_WD-WXA1E171A1KU', mountpoint '2TB' removed successfully.
Mar 17 18:54:29 Tower1 nginx: 2018/03/17 18:54:29 [error] 5672#5672: *698491 connect() to unix:/var/run/ttyd.sock failed (111: Connection refused) while connecting to upstream, client: 192.168.1.130, server: , request: "GET /webterminal/ws HTTP/1.1", upstream: "http://unix:/var/run/ttyd.sock:/ws", host: "1ad7a6e4386dab50134fcb40b4490f1f43e4ce85.unraid.net"
Mar 17 18:54:39 Tower1 nginx: 2018/03/17 18:54:39 [error] 5672#5672: *698548 connect() to unix:/var/run/ttyd.sock failed (111: Connection refused) while connecting to upstream, client: 192.168.1.130, server: , request: "GET /webterminal/ws HTTP/1.1", upstream: "http://unix:/var/run/ttyd.sock:/ws", host: "1ad7a6e4386dab50134fcb40b4490f1f43e4ce85.unraid.net"
Mar 17 18:54:49 Tower1 nginx: 2018/03/17 18:54:49 [error] 5672#5672: *698613 connect() to unix:/var/run/ttyd.sock failed (111: Connection refused) while connecting to upstream, client: 192.168.1.130, server: , request: "GET /webterminal/ws HTTP/1.1", upstream: "http://unix:/var/run/ttyd.sock:/ws", host: "1ad7a6e4386dab50134fcb40b4490f1f43e4ce85.unraid.net"
tower1-diagnostics-20180322-1714.zip