Linux does not see sdc on boot (but does during install)
OK, now I'm at a loss.
I have been struggling with getting my Ubuntu server to boot. After a couple of days of fighting with it, I gave up and reinstalled thinking that'll sort it out.
What I get is a kernel panic (the same as when I tried to fix things) saying that boot can't find sdc2 (where root is located, sdc1 is /boot). It only offers me the partitions for sda and sdb drives, but not sdc. But here's the kicker: I just installed the system and I definitely could see sdc!
Reason I wouldn't want to mess up the partition table is that I have already set it up (and I have a RAID5 setup as well that I don't want to accidentally mess up).
How is this even possible? It does look like the order of the disks has somehow changed (because I'm pretty sure I had boot and root on sda - although I'm not 100% sure but if not, I don't know what I was thinking). Trying to change the boot order in BIOS did nothing, I get exactly the same setup during install.
EDIT. A couple of more specific questions:
1. What determines the order of the devices in Linux? I.e. /dev/sda, /dev/sdb etc. as well as (hd0,gpt1), (hd1,gpt1) etc? gpt parts is easy enough (order they are on the disk), but it seems these can even be different (sda == hd1 and sdb == hd0).
2. Any idea why kernel doesn't see sdc but sees the other two devices?
3. Do I need the bios_grub flag on one of the partitions? System does attempt to boot without it.
I have pictures of the boot error, /etc/fstab and blkid, but seems I'm not allowed to post links to other sites.
I have tried to reinstall GRUB, edit grub.cfg directly, change parameters in boot menu ('e' in grub menu), reinstall the whole system, change boot order in BIOS menu and.. I can't even remember what I have tried (my initial attempt was a couple of weeks ago).
Before reinstall /etc/fstab said boot and root were on sda rather than sdc, but something must have messed up the order the disks are reported. But even in this case, why does this not work? I thought I could organize the partitions as I want.
Now I'm running out of ideas. Do I go and find 4 terabytes of backup storage somewhere, copy the RAID5 data there and wipe the whole system clean? Or just change boot and root to sda and home to sdc and re-format every partition apart from the RAID partitions (I didn't re-format during the re-installation)?
I'm also slightly worried how to rebuild the RAID array, since it didn't occure to me to backup mdamd.conf before re-installing the system.