The web site of WD for your area states the warrantyfor WD Cariar Black HDDs, for component parts or retail package HDD's is 5 years.
That's the same here in the US. It has nothing to do with the retailer, any problems or RMA's are between the consumer and WD.
They have a warranty check button, where you put the SN of the drive in, and it gives you that drive's warranty. Of course you have to have the HDD to have the SN!
I am comfortable with that, but if you want to be sure, here is the WD telephone number in Thailand
00-1800-4410570 Monday - Friday 10 am - 7 pm ST
Also for your area here is the email address you could use if needed.http://websupport.wdc.com/rdsfdc.asp?linktype=home&portaltype=wd&custtype=end&fs=&ss=&lang=en
I like the WD Caviar Blacks, never had a problem with them. Did have 1 Older IDE PATA 500GB HDD slow down last year, RMA'd it with an HD Tune Pro graph and they sent me a new one in 2 days, no questions asked.