1. The HEALTH of the hardware. For a very long time you had to wait to see trouble to surface. Now you can see some failures looming in the S.M.A.R.T. values. I am not going to breach what this is or the values there. That's for you, google and a few weeks of research.
2. The FILE SYSTEM integrity.
Now this is a more common failure as many USB drives can be unplugged during some write and BLAMMO, file system damage. There's CHKDSK (Windows), fsck (Linux and other OSes) but file loss only occurs when there are no backups.
In closing, there is no system today for everyday consumers to use on their PCs and USB drives.
If you did want to move to Enterprise grade storage consider deploying a Cloud compute or storage cluster in your home or shop.
Quite a long time postponed, I must finally do and determine the status of some portable hddrives connected via usb2 / 3 ports on different computers. These disks are quite often used for data transfer (without PC connection to network). I have all the important things on them. Of course, they are backed up. After connecting some hdds reports the need to perform a checkdisk. A few years ago I foolishly did this, with the fatal consequence of destroying some of the data without repair.
What is your favorite procedure/program for finding out if the hdd is before the end of its life, with the possibility of marking bad sectors, etc. It is not worth me for some money, which I will possibly give for a new hw. But I want to find out.
thanks for the advice