Why would a drive spontaneously from being /dev/sdb to /dev/sda? mode

[Robert Heller]

At Sun, 29 May 2022 17:27:02 +0100 "Ubuntu user technical support,? not for general discussions" <ubuntu-users at lists.ubuntu.com> wrote:

> 
> I recently was doing some [re-]configuration of my Lenovo Thinkpad
> running [x]ubuntu 21.10 and it failed to reboot.  After a bit of a
> worrying interval and lots of failed boots I found that an added disk
> drive that has been /dev/sdb1 for a long time (a year and a half or
> so) has become /dev/sda1.
> 
> Since /dev/sdba (or now, /dev/sda1) isn't actually necessary for the
> system to run I just commented it out of /etc/fstab and the system now
> boots OK.
> 
> However, some questions:-
> 
>     Why did it decide to change from /dev/sda to /dev/sdb?  Yes, I
>     know I can avoid the problem by using a UUID for the drive in
>     fstab but it would have been nice if the problem hadn't happened.

Who knows? My first guess is that /dev/sda died (see below). The thing is, the
hard use of device names in /etc/fstab has been depreciated for a very long
time now. You should *never* use /dev/sd<mumble> in /etc/fstab. *ALWAYS* use
UUID= (or even better LABEL=).

Some possibilities of what can cause drive names to change:

The presence or absense of removable media (like thumb drives).  And which USB 
port is used.

BIOS setting changes.

Driver updates.

Random timing in when devices become available.

Hot swapped disks being moved from slot to slot.

RAID disk failure.

> 
>     Why didn't the system boot?  When I tried to boot in maintenance
>     mode I could see the 90 seconds timeout ending but nothing
>     happened afterwards.  Surely, after the timeout, the boot
>     should/could continue?  ... and again, yes I know there's options
>     to add in fstab to say ignore mount failures.

My *guess* /dev/sda died or is dieing.

> 
> 

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