I just notice that one of my 4TB WD RED (few years old) has different size

It's the one that I paid $70 cheaper (It's already $20 cheaper than other local shop and I won $50 voucher for that shop)

normal WD RED = 4,000,787,030,016

suspected OEM WD RED = 4,000,000,000,512

 

First thing I check is HPA = disabled. already preclear 2 times and no error.

and I already filled half with no error.

I also asked on other forum and someone suggest to do DCO reset,

but I heard it's dangerous and can render drive unusable.

 

according to wd warranty page "out of region",

Is it OEM drive ? drive from WDC NAS ?

Fundamentally it doesn't matter => as long as you're not using this drive as a parity drive, the few extra bytes it's missing are irrelevant.

 

If you DO want to restore it to the max size, I'd use the free HDAT2 utility.

http://www.hdat2.com/

 

Just create a bootable CD or floppy (if you have one) and you can easily remove any DCO and/or HPA from the disk, restoring it to its full size.    But as I noted, there's really not much reason to do this.