Hard Disk Monitoring

My drive initially reported 8 weak sectors. I then tried repairing it and it turned out to be bad. I have questions about reallocated sectors 1- Do we need to have data in that sector for reallocation to occur? Or does it reallocate even if there is no data in it? -2Initially my old disk had 8 bad sectors, I read them and there were no problems in testing. However, when I tested again 5 days later, there was a bad sector. Is this because the head hits the plate and the inner surface of the drive gets dirty and spreads to other places?

Generally the sector can be reallocated when it is accessed by the disk drive heads. Usually this happens when a write operation targeted the appropriate sector, but sometimes can happen on a read command too.

So generally no, we do not need "real" data in the appropriate sector in order to detect, reveal and fix the sector.
For example, the Disk menu -> Surface test -> Read test designed to reveal possible issues and the Disk menu -> Surface test -> Disk Repair designed to force the drive to stabilize: reallocate the sector if required (even if the sector contains no data).
In some cases (especially if the number of problems is relatively higher) the more intensive Reinitialize Disk Surface test required (careful: this clears all sectors on the drive. A simpler / less effective function usually called incorrectly as "low level format" in other tools).


> However, when I tested again 5 days later, there was a bad sector.
> Is this because the head hits the plate and the inner surface of the drive gets dirty and spreads to other places?

There is good chance for that. Usually relatively smaller number of bad sectors can be acceptable, as explained at
https://www.hdsentinel.com/faq.php#health
but if a drive has any number of bad sectors - we can expect even more later.

In this case, I always recommend to
- verify the operating environment / conditions: check cables, connections, power supply, power cable - because these can cause unstable operation and can result bad sectors (or even more serious failure)
- then (after backup) perform the above mentioned Disk menu -> Surface test -> Reinitialize Disk Surface test
By its nature it is more effective to force the drive to recognise problems easier and re-allocate the sectors which can damage / fail later.
It is better to reallocate during the test (to prevent later use) than detect problem(s) when the affected sector may contain important data.

As always recommended, if you use Report menu -> Send test report to developer option, it is possible to check the actual disk drive status / problems / Health %
You may send multiple reports, eg. once as a "base" and later if you see any change (for example after a test and/or normal use) as then it is possible to compare and verify any differences.