I don't know why there's 1.0 MB at the top of sdb - I selected "Beginning" for the 521 MB partition.

SCSI1 (0,0,0) (sda) - 400.1 GB ATA THNSFxxxxx
    #1  primary  510.7 MB   K  raid
          pri/log    399.6 GB        FREE SPACE
SCSI3 (0,0,0) (sdb) - 400.1 GB ATA THNSFxxxxx
                           1.0 MB       FREE SPACE
    #1               510.7 MB   K  raid
                       399.6 GB        FREE SPACE

I look forward to reading your procedure for a correct setup.

I have backup covered now (Deja Dup). At least that piece of the puzzle appears to be stable.

Thanks!

EDIT: Just rebooted into my User account vs Root and the server is also working OK, so it's not a difference between accounts (permissions, etc).

I found just this, which may be helpful ...

Source: https://forums.debian.net/viewtopic.php?t=137068

EDIT 2: Is this telling me anything relevant?

root@devuan1:~# df -T -h /etc/inittab
Filesystem     Type  Size  Used Avail Use% Mounted on
/dev/sda2      ext4   44G  4.0G   38G  10% /
root@devuan1:~# 

Anyone using BIND or Knot Resolver as a DNS resolver plus DNSdist as a DNS load balancer in Devuan?

Any reason doing so would be a bad idea in Devuan?

It's her ("linuxbabe") fault that I'm looking into this ... https://www.linuxbabe.com/ubuntu/dns-over-https-doh-resolver-ubuntu-dnsdist  lol

Do I read correctly that writing to a "local filesystem" would include a USB drive?

QUESTION: What is the recommended app, or command line string, to use to backup to the 1TB external drive, please?

Gnome Disk Utility looks promising.

dd would be OK ... unless over-tired and the wrong string is typed ...

Clonezilla and Tar also look interesting. https://www.maketecheasier.com/back-up-entire-hard-drive-linux/

Timeshift doesn't seem to save everything.

OK. So, basically, start from scratch.

@ralph_ronnquist what would be the equivalent-function mirroring method to Raid1 that isn't Raid1?

Is the alternative a complex process and one that requires extra attention? (I really want to get to some long-delayed content. This is my second attempt at a server - I sold the other hardware as it was way beyond what I needed and frustratingly complex.)

Is anyone up to walking me through setting up mdadm RAID1 (and making sure that the BIOS raid is disabled)?

OR, should I just follow this?

https://linuxconfig.org/linux-software-raid-1-setup

Note: I've just dedicated a 1TB external drive for backup purposes. That way the Raid1 array maintains a mirror and the external drive a backup. I guess I'll just go ahead and follow the instructions from the link and then see about the best way to implement the backup (I'd like to run it more often than 1x/day.)

I've been reading about sync ...

Is it possible that looking here ... https://linuxconfig.org/linux-software-raid-1-setup

... scrolling down to Configure persistent RAID mount ...

that the missing line in /etc/fstab "/dev/md0  /mnt/raid1  ext4  defaults  0  0" is the cause?

Is it correct that without this I don't have a working RAID 1 array that stays mounted even after a system reboot.

Could that cause the lost changes I'm experiencing?

Anything here look suspect, please?

root@devuan1:/etc/nginx# parted -l
Warning: Not all of the space available to /dev/sda appears to be used, you can
fix the GPT to use all of the space (an extra 6320 blocks) or continue with the
current setting? 
Fix/Ignore? I                                                             
Model: ATA THNSF8400CCSE (scsi)
Disk /dev/sda: 400GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system     Name  Flags
 1      17.4kB  538MB   538MB   fat32                 boot, esp
 2      538MB   48.5GB  48.0GB  ext4
 3      48.5GB  56.5GB  8000MB  linux-swap(v1)  swap  swap
 4      56.5GB  400GB   344GB   ext4

Warning: Not all of the space available to /dev/sdb appears to be used, you can fix the GPT to use all of the space (an extra 6320
blocks) or continue with the current setting? 
Fix/Ignore? I                                                             
Model: ATA THNSF8400CCSE (scsi)
Disk /dev/sdb: 400GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system     Name  Flags
 1      17.4kB  538MB   538MB   fat32                 boot, esp
 2      538MB   48.5GB  48.0GB  ext4
 3      48.5GB  56.5GB  8000MB  linux-swap(v1)  swap  swap
 4      56.5GB  400GB   344GB   ext4

It's not doing that on my server - it's creating a new one with only a few lines in the first.

It was, prior to today, also still adding to a log that already contained pages of log files - while also updating a new log.1.

I need guidance as to where to start looking for what's broken:

Raid 1

Devuan settings

??

Thanks

These are the last few lines of output from https://unboundtest.com for CAA.

Jan 05 03:47:24 unbound[729481:0] info: reply from <com.> 192.41.162.30#53
Jan 05 03:47:24 unbound[729481:0] info: query response was ANSWER
Jan 05 03:47:24 unbound[729481:0] info: validated DNSKEY com. DNSKEY IN
Jan 05 03:47:24 unbound[729481:0] info: resolving realupnow.com. DS IN
Jan 05 03:47:24 unbound[729481:0] info: response for realupnow.com. DS IN
Jan 05 03:47:24 unbound[729481:0] info: reply from <com.> 2001:503:d2d::30#53
Jan 05 03:47:24 unbound[729481:0] info: query response was nodata ANSWER
Jan 05 03:47:24 unbound[729481:0] info: NSEC3s for the referral proved no DS.
Jan 05 03:47:24 unbound[729481:0] info: Verified that unsigned response is INSECURE
Jan 05 03:47:24 unbound[729481:0] info: 127.0.0.1 realupnow.com. CAA IN NOERROR 1.528696 0 101