my system (standalone PC) can’t find the root device on boot. It drops to rescue shell.
When I run it the latter blkid, it does not list any partition at all.
This happens irregularly. Symtpom remains on warm reboot (CTRL + ALT + DEL).
It disappears on fresh cold boot (shutdown and new boot).

Hard drive is a SSD. The problem did exist with a non-SSD hard drive previously, too. Then it occurred with a non-arch system (Ubuntu 16.04) with the same mainboard.
The SSD is connected via SATA. Switching the ports (there are four) did not help (the earlier HDD did use SATA, too).
The mainboard is an ASUS A8V Deluxe. It’s from a time when IDE was standard and SATA emerged.

I suspect the problem is related to the (1) mainboard, (2) it’s SATA connection and (3) a newer linux kernel.

When did the problem occur?
After installation of antergos (4.6.2-1-ARCH) itself.

What did I try to solve the problem?

  • Ensure UUID is correct: Compare UUID from lsblk -o +uuid with /etc/default/grub.conf
  • Run mkinitcpio -p linux: https://bbs.archlinux.org/viewtopic.php?pid=1104821#p1104821
  • Ensure block precedes autodetect in HOOKS= in /etc/mkinitcpio.conf: http://superuser.com/a/788480/ (yep, I did the mkinitcpio -p linux after that)
  • Ensure ahci sdmod is in MODULES= of /etc/mkinitcpio.conf (yep, did the mkinitcpio -p linux after that)
  • Add iommu=soft to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub.conf, then do grub-mkconfig -o /boot/grub/grub.cfg, grub-install /dev/sda
  • Change BIOS settings: Disable quick boot, Enable/Disable APCI 2.0, Reset to Setup Defaults

What can I exlude?

I could not save output of dmesg from rescue shell because I have no file system available.
The system recognizes an USB stick, however does fail to mount it: It fails if I provide -t vfat.

Which information do you require to identify the problem further?
What do you suggest (beyond switching the motherboard itself) I should do to solve the problem?

Thanks for your help.