Configured System:

HPE DL20
1x 480GB SSD
3x 960GB SSD

I am installing Debian Linux on servers using UEFI PXE and a preseed file
for a touchless installation. This has been our standard method for Debian
installs for years, starting with "buster." It has worked VERY reliably for
us.

When using the same method to install Debian 12, I am noticing that the
installer is detecting the drives out of order. It does not match what the
server BIOS or HPE ILO5 displays. With each PXE installation attempt the
ordering can vary. Looking in /dev/disk/by-path you can see the symlinks
differ between install attempts. Sometimes the order matches the PCI bus
reference and sometimes it's jumbled up.

This is an issue when you want to tell partman to use /dev/sda (the first
drive) for the installation and have grub installed properly on /dev/sda.
This is even worse when trying to do a software RAID1 via preseed. The
pairs of drives are not being selected in a predictable fashion.

Interestingly enough, after the installation is complete and the Debian 12
system is booted up, it always shows the drives in the proper order, 100%
of the time. But the boot media may or may not be the correct drive. This
is only an issue at install time.

This past week I performed dozens of PXE installs on a set of 3 servers.
Debian 11 had no problems. Only Debian 12 displayed this behavior on each
of the 3 servers. I tried updating firmware on all 3 servers so that it is
running the latest versions, but that had no effect.

AFAIK /dev/sd* discovery and ordering was never guaranteed to be
deterministic nor persistent across boots nor match any hardware or
firmware ordering. One should not rely on these names, hence the use of
persistent identifiers such as UUID, device path or disk ID.

I advise to not hardcode /dev/sd* anywhere and use persistent
identifiers instead.

I agree. That is why I used UUID for the fstab entries. But this drive
ordering issue is specific to the installer. The preseed is expecting
a /dev/sd* type of entry in order for partman to partition the correct
drive...or in my case (using software RAID1) drives.

As stated above, I am not using /dev/sd* anywhere other than in the
preseed which requires it.

If I understand correctly, the issue is not drive ordering but the
preseed capability to handle persistent drive identifiers.