How do I really find the health of a hard drive?

[Plecto]

Hello. I've been playing around with a FreeNAS build and for that I bought a bunch of second hand 2TB drives. As I don't really know the state of these drives, I've downloaded different kinds of hard drive health software to try to get an idea, but I'm having a hard time interpreting the results. Most of the drives I've tested seems to fail when running SeaTools for Windows, but pass all other tests. CrystalDiskInfo gives a "pass", while SeaTools for Windows gives a "fail" when running SMART test or Long Generic which I find odd. I just now got a critical error from my FreeNAS build saying "Offline uncorrectable sectors" on one of the drives after running a scrub. I replaced the drive and put the faulty drive in my Windows computer, ran CrystalDiskInfo which told me that the disk was Good, windows error checking tool also found no errors. How do I know what software I can trust and not? What is the ultimate way to stress test a hard drive to figure out if it's okay or not?

The NAS I have doesn't really contain any critical data, that is the reason why I'm playing around with second hand hard drives like this.

[fzabkar]

Bad sectors are transparently reallocated. This means that the OS may never see them, especially when they are discovered by the drive's own internal background scan.

GSmartControl reports the drive's internal error logs, in addition to the SMART data.

You can scan the drive for "slow" sectors with tools such as Victoria, HDDScan or MHDD (DOS).

[Plecto]

Thanks for the reply. I ran a complete write+read test (destructive) on the drive. After about eight hours all dots came back green, no errors. Is it common for a drive to fail all SeaTools test, but pass all others? I don't get whats going on.

The number of reallocated sectors is a SMART parameter, right? CrystalDiskInfo told me that the RAW value for this was zero.

[fzabkar]

Are any of the drives in external enclosures?

[Plecto]

Yes. I'm using a Deltaco S-ata to USB docking station.

[fzabkar]

SeaTools has trouble seeing drives in some USB enclosures.