my friend whom is in the storage industry just dropped this bit of wisdom on me I thought you guys might be keen to know:
That is true. When I worked at TiVo many years ago I did a lot of hard disk quals and learned a lot about drives. The 40GB and 80GB were the same drive. A one platter drive only one side of the platter didn't pass QC. The 160GB was a 2 platter version of the same drive and again it came in a 120GB model that was 3 good sides of 2 platters.
A lot has changed in hard drives since then, but the point remains the same.
I'm not sure if it really matters. The portions of the drive surfaces you get in any of the models are just fine and I don't know if it is any indication of potential failure.
I learned a few things from those days.
1) How the drive is handles is directly related to how long it'll last. Buy retail box drives with full packaging, never buy bulk were someone has (mis-) handled it. I'll never use a pre-handled or used drive in any mission critical situation. It WILL fail in 2 years.
Treat hard drives like they are eggs. Don't remove it from the box until you're ready to install it and just handle it like (again) it's an egg. Even just setting it down on a hard table can result in damage that you won't see for a year. I'm not kidding, the G-forces from even a gentle table impact is enough to cause damage (it's ridiculous.) Try to set it on a cloth or just be super gentle. I know this sound ridiculous, but I've seen the proof. I handled a lot of drives in those days and the ones that weren't handled gently all came back to me 9 months later as dead. Normally I treat a lot of warnings like people are being overly cautious, but trust me on this one. I'll never criticize anyone for being too gentle with HDD.
Once they are installed in the unit, don't slam it around. It's not as fragile in the case since the unit absorbs most of the shock. Also try to avoid moving it while the drives are powered up and spinning. This is when movement will slam the heads against the platter causing a few microns of scrape off, which eventually that dust causes the damage months later. I've seen the actual test result data.
2) Frequent starts and stops is not good. Letting a drive power down in a PC is fine but set it to a long time like 2 hours so that it only powers down when the PC is left idle for hours on end.
3) The above doesn't apply to laptop hard drives. They're built to handle abuse when not spinning and a lot of power up/downs.
A lot of people have different experiences with the same manufacturers or drive models, and I bet most of those complaints are due to handling.
When it comes to my NVR drive, I'm not terribly concerned with reliability. It's just surveillance footage. As long as it doesn't fail right after something bad happens I can probably live without the footage.