I am a long-time linux user, for the last 10 years or so have been using linux mint. Recently I have decided to switch to manjaro and after trying it on my laptop for a month I have decided to install in on my desktop, too.
I have a Gigabyte 970A-DS3P motherboard with amd fx 8350 - not the latest hardware but still powerful enough. I have 5 disks in my computer - 2 SSDs (500GB and 250GB - the larger one is used for system) and 3 HDDs (1TB, 2TB and 3TB - I'll call them disks 1, 2 and 3).
Everything started smoothly, after the OS installation I installed additional packages and configured the system and then I rebooted it. From that point my HDDs 1 and 2 were gone - gnome disks showed them as 'unknown' partitions. Suspecting further problems I immediately disconnected disk 3 and then tried to recover disks 1 and 2. Testdisk found lost partitions but could not recover them. At first I thought that my motherboard or disks broke and I put HDDs in another computer. From there I could recover my files and copy them elsewhere but when I returned disks to my computer I could not create new partitions. Gnome disks, Gparted, fdisk and gdisk complained that the partition table was missing but could not write one. I then started gparted distro on another computer and could restore partition tables there.
I reinstalled linux mint on my desktop and tested disks and everything went smoothly. I restored the data, then tried to reinstall manjaro and the same thing happened again. After the first reboot all HDDs were gone - this time deleting partition table on disk 3 also. SSDs were not affected in any way.
After a long weekend of trial end error I found the problem that is 100% reproducible. My motherboard seems to not play nicely with linux but so far the only problem has been usb3 not working and slower startup times which could be prevented by sending "iommu=soft" switch to kernel. If that switch was not set I wouldn't have usb3 support and that was it.
However, in latest manjaro (18.1) failing to send that switch to kernel will lead to partition table deletion in all HDDs. First boot after install seems to work but after the first reboot the disks would lose their partition tables. None of the partitioning tools that I've tried (gparted, gnome disks, fdisk, gdisk, testdisk) could create partition table on those disks afterwards and I was able to create partitions only from gparted distro with "iommu=soft" switch sent to kernel. If the "iommu=soft" switch is immediately added to kernel everything would work.
I do not know if this is a newer kernel bug or is something manjaro specific but I think that those with AMD FX cpus and this motherboard need to be warned.