Am 2020-06-12 20:25, schrieb richard lucassen:
> Try to add "nofail" or "noauto":

nofail was a good hint. Now the system boots, but the usb disk is still
not mounted. "mount -a" mounts it without errors after boot.

I see no errors in /var/log/boot and dmesg.

The only messages concerning this drive:

[    4.153932] scsi 0:0:0:0: Direct-Access     WD       Elements 25A3    
1021 PQ: 0 ANSI: 6
[    4.159536] sd 0:0:0:0: [sda] Spinning up disk...
[    4.161466] sd 0:0:0:0: Attached scsi generic sg0 type 0
[   22.522458] sd 0:0:0:0: [sda] Very big device. Trying to use READ 
CAPACITY(16).
[   22.524863] sd 0:0:0:0: [sda] 19532808192 512-byte logical blocks: 
(10.0 TB/9.09 TiB)
[   22.532067] sd 0:0:0:0: [sda] 4096-byte physical blocks
[   22.538598] sd 0:0:0:0: [sda] Write Protect is off
[   22.541988] sd 0:0:0:0: [sda] Mode Sense: 47 00 10 08
[   22.542724] sd 0:0:0:0: [sda] No Caching mode page found
[   22.547320] sd 0:0:0:0: [sda] Assuming drive cache: write through
[   22.554350] sd 0:0:0:0: [sda] Very big device. Trying to use READ 
CAPACITY(16).
[   22.983388]  sda: sda1
[   22.984576] sd 0:0:0:0: [sda] Very big device. Trying to use READ 
CAPACITY(16).
[   22.989231] sd 0:0:0:0: [sda] Attached SCSI disk