Stretch installation: thumb drive recognized as /dev/sda
I installed Stretch on my Thinkpad from a USB flash drive. Only after the
installation, during the first boot did I notice that something was wrong. GRUB
failed to load the kernel and after a short diagnosis I learned that for some
reason, the Debian installer saw my USB thumb drive as /dev/sda and the SSD as
/deb/sdb. This caused GRUB config to be wrong when I removed the flash drive
I did some testing and apparently, if I booted the Debian installer from my
Thinkpad X220's only USB3 port, it would be recognized as /dev/sda, and if I
used a USB2 port, it would be /dev/sdb.
Doesn't the Debian Installer/GRUB not use UUID? What caused the problem here?
I've never experienced such a fail before or since but it did cause some
confusion and made me reinstall.
 FWIW, apparently only (some of?) the i7 models of X220 have a USB3 port.