Just bought 5 used 8TB Ultrastar drives on ebay for only $35 each. Heck of a deal right? Checked smart info and everything looks good. Of course i know it would be a good idea to do a complete scan for bad sectors but I don’t know the best program for that. Ideally a free win10 program that i could test all 5 at once connected to one pc
ZFS scrubs. I sleep well at night and haven’t lost a byte of valuable data in 15+ years.
None. Modern drives reallocate bad sectors so the only important metric I look at is remaining spare sectors.
Do a long SMART test. It goes over the whole drive. The short ones only do spot checks.
Any drive made this side of year 2000 will check itself when reading, so all you need is to fill it with junk data and open it, then delete.
The manufactures software. In your case
https://support-en.wd.com/app/products/downloads/softwaredownloads
WD Drive Utilities
Western Digital Dashboard
It is expected that some sectors fail over time. The HD is provision with extra space to account for this. The SMART threshold is what you should look at.