588. ata6: SRST failed (errno=-16) AND disk-by-uuid does not exist

The problem:
I've been having boot issues with one of my nodes. Everything is fine up to and past GRUB:

Then this happens:

[21.405411] ata6: SRST failed (errno=-16)

And typically I get dumped in a shell:

ALERT! /dev/disk/by-uuid/xxxx does not exist

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Towards the solution:
blkid shows both disks:

blkid

Either way, turns out the way to get the system to boot is pretty simple. Type exit and hit enter.

exit leads to successful boot

Looking at dmesg this is what happened:

[    1.998149] usb 2-1: Product: USB Optical Mouse
[    2.005374] input: USB Optical Mouse as /devices/pci0000:00/0000:00:12.1/usb2/2-1/2-1:1.0/input/input1
[    2.005452] hid-generic 0003:0461:4D81.0002: input,hidraw1: USB HID v1.11 Mouse [USB Optical Mouse] on usb-0000:00:12.1-1/input0
[    6.476845] ata6: link is slow to respond, please be patient (ready=0)
[   11.465026] ata6: device not ready (errno=-16), forcing hardreset
[   16.665379] ata6: link is slow to respond, please be patient (ready=0)
[   21.485411] ata6: SRST failed (errno=-16)
[   26.685767] ata6: link is slow to respond, please be patient (ready=0)
[   31.505806] ata6: SRST failed (errno=-16)
[   31.894576] uhci_hcd: USB Universal Host Controller Interface driver
[   36.706152] ata6: link is slow to respond, please be patient (ready=0)
[   66.579156] ata6: SRST failed (errno=-16)
[   71.611367] ata6: SRST failed (errno=-16)
[   71.623705] ata6: reset failed, giving up
[  105.133562] PM: Starting manual resume from disk
[  105.133565] PM: Hibernation image partition 8:2 present
[  105.133567] PM: Looking for hibernation image.
[  105.133775] PM: Image not found (code -22)
[  105.133777] PM: Hibernation image not present or could not be loaded.
[  105.189165] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)
[  107.565728] udevd[725]: starting version 175

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Fixing it:
Increase the rootdelay so that the harddrive(s) have time to boot up. I think in my case the issue is that I found an ancient IDE drive which may be slow to spin up, and maybe even failing (I use it for /scratch).

Either way, edit /etc/default/grub and add rootdelay=90 (for example) to the end of GRUB_CMDLINE_LINUX_DEFAULT, e.g.

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=0x0318 text rootdelay=90"

Then do

sudo update-grub

and hopefully the next time your system will boot, although slowly.