HDD disappearing

I'm without ideas! This is NOT an issue that belongs to openWRT I think, but because I'm without options and knowing there are a lot of smart people here online, asking for help here.

The case:
I had 3 servers: 2 in Europe and 1 in Russia.
They are connected using openWRT and openVPN
Connection between the servers was 5MBps at worst. ~ 40Mbps.. (From here on I only write in Megabits per second)
usually 80+ Mbps though.

Never had a problem here. All 3 servers are backups for the data. So I backup always local
in my own home to the server, and 1 backup to the other server in Europe and 1 backup to the server in Russia.

Now I moved to Southeast Asia and the situation is as follow:
I have 3 servers: 1 in Southeast Asia, 1 in Europe and 1 in Russia.
the connection from Southeast Asia to Europe&Russia standard ISP routing is 1Mbps and using VPN through VPN through VPN I get 10Mbps.
the connection goes from Malaysia to Singapore to Saudi to Europe.

Reading data from the disks works without problems. I can ready 1 TB of data no problem.
But writing, that's different. writing data to disk over the ISP connection with 1Mbps speed every 10-20GB the disk being written to over the VPN (wrting data from Asia to Europe/Russia) the disk just disappears! It's gone. Shutting down and restarting the computer the disk is back.

I tried all kind of test tools, complete write/read every single bit of the disks, every 100% ok!
And locally I can copy back and forth data between disks non stop. No errors.

the disks ONLY DISAPPEAR when I write data to them over the slower vpn connections!
using the 10Mbps connection, the disks disappear every 50GB..

So the slower the speed to write to the disk, the sooner the disks just disappears.

And writing locally, from one disk to the other, it never happens..

I must say, this only happens to these disks:
Seagate ST8000AS0002

All the other disks from Seagate and WD don't have this issue. Only the ST8000AS0002 of which I have 20+ and all these disks have this issue.

I contacted Seagate about this and they "said' they forward this to technical department. Well I can't be sure they really forwarded it. Maybe they just tell me they did without doing so.

Is this an issue that could be something in the firmware of these drives?
could it be something in VPN?
could it be some DPI by ISP or censorship in other countries sapping on the connection?
Censorship here in Asia?

I have really no idea what could cause this.

Again, writing to an ST8000AS0002 locally at 400Mbps I can copy 1TB, 8TB, no issues.
writing over 40+ Mbps openVPN connection in Europe to an ST8000AS0002 no issues. 1TB, 8TB works just fine

writing over 10Mbps openVPN connection in Asia to an ST8000AS0002: disk disappearing every 50GB and only shutdown/start computer disk comes back.

writing over 1Mbps openVPN connection in Asia to an ST80000AS0002: disk disappearing every few GB and only shutdown/start computer disk come back.

Only happens to ST8000AS0002.

Add: i did switch SATA cables, power supply, power cables, etc.
I tried different SATA controllers, different motherboards

I searched all over internet, used google, yandex, yahoo.. no one seems to have this issue or at least
I didn't find anyone, maybe my setup is something special not common..

anyway, anyone an idea what this might be?

May I know where did you connect the HDD to? The one running OpenWrt or some other servers?

Hi Rtau,

thanks for asking. The setup is the same everywhere and as follow:
Windows Server 2012 R2
The HDD are all connected using SATA on the motherboards so they are build-in the computer directly to windows
Windows Server 2012 R2 have all 2 network cards. 1 is for the WAN and 2nd card for the LAN
WAN is usually directly to ISP (at one location behind the router of ISP because of the necessity of VLAN tagging which doesn't seem to work on my installation)
LAN is always 172.22.x.x/16 each segment of the VPN their own /24 part of that /16 network
So the network in Asia is 172.22.64.x/16 and the network in Europe 172.22.56.x to 172.22.63.x / 16
and the network in Russia 172.22.67.x to 172.22.69.x /16

The /16 does add a little bit of overhead true, but easier for me when every device can freely communicate.

Anyway, the Server2012R2 has VirtualBox of oracle installed and here is where the openWRT are running.

Purely as virtual router, to translate between WAN and LAN and the LAN port on the Windows servers is then connected to switched 16-32 port switches.

So all connections always go to the WAN port on the windows servers. The virtualbox openwrt is bridged and incoming VPN goes to the virtualbox openwrt and from there it builds up the VPN network.

So the server on one end of the VPN can through this VPN connect directly to the server on the other end of the VPN.. from LAN to LAN the traffic goes through the tunnel.. so WAN is used purely for setting up the VPN tunnels.

I hope I explained it understandable, I doubt I would understand it myself if I hadn't set it up myself.